<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:b0687adf-f233-4763-8286-aa1d7a94b927,g:786f20ff-befb-4927-a6da-c8cec2ba3b71-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.appfolio.com/role/Cover" xlink:type="simple" xlink:href="appf-20211231.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/Cover" xlink:type="extended" id="i5e7fc46d6e1e4542ad1021216c7d4cb2_Cover">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_0c503851-0b63-48ff-b16b-9da25804299f" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentType_0c503851-0b63-48ff-b16b-9da25804299f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAnnualReport_bd675ada-45ca-41e9-bf02-7835100e7f3c" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentAnnualReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentAnnualReport_bd675ada-45ca-41e9-bf02-7835100e7f3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_d1ba13b0-7187-43ce-8fe0-e06d30590c35" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentPeriodEndDate_d1ba13b0-7187-43ce-8fe0-e06d30590c35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_88753f9e-cdbf-4d99-8241-b1ad1b40eb8b" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_CurrentFiscalYearEndDate_88753f9e-cdbf-4d99-8241-b1ad1b40eb8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_6c2578d2-1dbf-4fb6-8e23-e9961437f476" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentTransitionReport_6c2578d2-1dbf-4fb6-8e23-e9961437f476" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_6076950a-b281-4aaa-a688-ae100d6dbd91" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityFileNumber_6076950a-b281-4aaa-a688-ae100d6dbd91" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_2edd2dc2-e91a-4286-9c5a-9f66b64185ce" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityRegistrantName_2edd2dc2-e91a-4286-9c5a-9f66b64185ce" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_e71e459c-070a-4f49-8b90-d0ea14ae53ff" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityIncorporationStateCountryCode_e71e459c-070a-4f49-8b90-d0ea14ae53ff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_e3084276-4b4c-4c49-8fa0-53af6019b9d7" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityTaxIdentificationNumber_e3084276-4b4c-4c49-8fa0-53af6019b9d7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_31146b2c-8616-400f-bc3e-ab19762d72f9" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityAddressAddressLine1_31146b2c-8616-400f-bc3e-ab19762d72f9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_2ba8b413-3783-48f0-b1a1-ff5fc658cbbb" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityAddressCityOrTown_2ba8b413-3783-48f0-b1a1-ff5fc658cbbb" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_23f970d0-9d73-4428-9cc6-11040c62312b" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityAddressStateOrProvince_23f970d0-9d73-4428-9cc6-11040c62312b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_31334b2b-3f7c-4ca9-8167-054cf975fcb7" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityAddressPostalZipCode_31334b2b-3f7c-4ca9-8167-054cf975fcb7" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_271e3ca2-3d88-4f26-80f8-15e62dc6d528" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_CityAreaCode_271e3ca2-3d88-4f26-80f8-15e62dc6d528" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_4f79e101-fe1d-473f-a8b6-68067f07d7a1" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_LocalPhoneNumber_4f79e101-fe1d-473f-a8b6-68067f07d7a1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_4af665cb-63e6-4fc0-acea-d066c92305f3" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_Security12bTitle_4af665cb-63e6-4fc0-acea-d066c92305f3" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_27d8e97a-c713-4c13-9014-3a8e5ba57665" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_TradingSymbol_27d8e97a-c713-4c13-9014-3a8e5ba57665" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_8c453b6a-c934-439a-b72f-1de06aa6f86b" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_SecurityExchangeName_8c453b6a-c934-439a-b72f-1de06aa6f86b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityWellKnownSeasonedIssuer_169bc304-ec43-497c-ad75-097d58c096dc" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityWellKnownSeasonedIssuer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityWellKnownSeasonedIssuer_169bc304-ec43-497c-ad75-097d58c096dc" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityVoluntaryFilers_4242cd91-99b2-4da7-b477-a5b491e307a6" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityVoluntaryFilers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityVoluntaryFilers_4242cd91-99b2-4da7-b477-a5b491e307a6" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_5ac3e1f8-2ffb-45de-9993-0c80c73cb189" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityCurrentReportingStatus_5ac3e1f8-2ffb-45de-9993-0c80c73cb189" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_291a6dc2-a4e8-42b8-8bb6-7e0fad0a332d" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityInteractiveDataCurrent_291a6dc2-a4e8-42b8-8bb6-7e0fad0a332d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_4f8cfc4b-c196-4f63-8f99-5bb39b93ba97" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityFilerCategory_4f8cfc4b-c196-4f63-8f99-5bb39b93ba97" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_9483c144-12ad-43eb-bcac-679605621f99" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntitySmallBusiness_9483c144-12ad-43eb-bcac-679605621f99" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_15c73aa8-785c-42c4-9891-1bbe121819dc" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityEmergingGrowthCompany_15c73aa8-785c-42c4-9891-1bbe121819dc" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag_5048db43-bbde-4735-97e9-e05ac2068040" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_IcfrAuditorAttestationFlag_5048db43-bbde-4735-97e9-e05ac2068040" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_4942e2aa-2bd1-41c6-8264-632faf66a3d6" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityShellCompany_4942e2aa-2bd1-41c6-8264-632faf66a3d6" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityPublicFloat_420f9b0c-a988-4532-a6c1-ab0176cbee97" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityPublicFloat_420f9b0c-a988-4532-a6c1-ab0176cbee97" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_7b3b3ba5-722a-44bb-bf2d-64b9697d6ee8" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_7b3b3ba5-722a-44bb-bf2d-64b9697d6ee8" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentsIncorporatedByReferenceTextBlock_54a8564d-a71f-4bc5-8001-af63e3d1d9a8" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentsIncorporatedByReferenceTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentsIncorporatedByReferenceTextBlock_54a8564d-a71f-4bc5-8001-af63e3d1d9a8" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_aad0510d-ece6-4ac6-9359-79268a5ca5cd" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_EntityCentralIndexKey_aad0510d-ece6-4ac6-9359-79268a5ca5cd" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_ed98dd4a-825b-44d6-810c-835aa1997339" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentFiscalYearFocus_ed98dd4a-825b-44d6-810c-835aa1997339" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_ef1df691-9b04-4665-a6c6-5fd048ec8289" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentFiscalPeriodFocus_ef1df691-9b04-4665-a6c6-5fd048ec8289" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_814ca55e-6f13-44b1-b874-208f3418f0d1" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_AmendmentFlag_814ca55e-6f13-44b1-b874-208f3418f0d1" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_b1837fd1-fc77-4e8c-8db0-b3f652a0e83b" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_8e79eb93-5e6c-4415-9c2d-d23d00d54d65" xlink:to="loc_dei_DocumentInformationTable_b1837fd1-fc77-4e8c-8db0-b3f652a0e83b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_26fc296a-1f62-4ee3-b213-46b957d890ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_b1837fd1-fc77-4e8c-8db0-b3f652a0e83b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_26fc296a-1f62-4ee3-b213-46b957d890ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_26fc296a-1f62-4ee3-b213-46b957d890ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_26fc296a-1f62-4ee3-b213-46b957d890ad" xlink:to="loc_us-gaap_ClassOfStockDomain_26fc296a-1f62-4ee3-b213-46b957d890ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5cceead3-a1d6-446e-865a-a3dc0dd5bf12" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_26fc296a-1f62-4ee3-b213-46b957d890ad" xlink:to="loc_us-gaap_ClassOfStockDomain_5cceead3-a1d6-446e-865a-a3dc0dd5bf12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_f8b7b848-b9e5-44ea-902b-4c02a35cef87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5cceead3-a1d6-446e-865a-a3dc0dd5bf12" xlink:to="loc_us-gaap_CommonClassAMember_f8b7b848-b9e5-44ea-902b-4c02a35cef87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_f5476fb4-5855-4dfc-9824-31765d24bc97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5cceead3-a1d6-446e-865a-a3dc0dd5bf12" xlink:to="loc_us-gaap_CommonClassBMember_f5476fb4-5855-4dfc-9824-31765d24bc97" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="appf-20211231.xsd#ConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/ConsolidatedBalanceSheets" xlink:type="extended" id="i439f296ca11040aaaf5b2c9e1db015f6_ConsolidatedBalanceSheets">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7389cd65-8478-4de3-b40c-959d7284448d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7389cd65-8478-4de3-b40c-959d7284448d" xlink:to="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_21117fc0-7f1a-4082-8a8c-15437ed5735b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_21117fc0-7f1a-4082-8a8c-15437ed5735b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_cd19bb31-c4bd-4aa4-8d7d-8451033dba85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_cd19bb31-c4bd-4aa4-8d7d-8451033dba85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_4ced351e-c99d-4585-a7af-97b3f812ac0d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_4ced351e-c99d-4585-a7af-97b3f812ac0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_5797a63c-1d56-4605-8fa2-5f4012ba9416" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_5797a63c-1d56-4605-8fa2-5f4012ba9416" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_0434c0dc-c336-435c-9028-702a42b4e5b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b28465ef-6c4c-4fc5-b1fd-8300f98d49e5" xlink:to="loc_us-gaap_AssetsCurrent_0434c0dc-c336-435c-9028-702a42b4e5b3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_bef6ad1e-2d13-4933-ad81-05d8e606b93d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_bef6ad1e-2d13-4933-ad81-05d8e606b93d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_a41a2854-ea49-4c0f-95ab-4237c7bb4472" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_a41a2854-ea49-4c0f-95ab-4237c7bb4472" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_2351d42e-5da2-4809-bfdd-30b1f8008a2b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_2351d42e-5da2-4809-bfdd-30b1f8008a2b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareNet_ffb0ed65-7dc2-4aa5-8429-fcc64b76e029" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedComputerSoftwareNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareNet_ffb0ed65-7dc2-4aa5-8429-fcc64b76e029" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_ce0a0062-ee2a-4b6a-bdc0-dd18d3ff7240" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_Goodwill_ce0a0062-ee2a-4b6a-bdc0-dd18d3ff7240" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_14cd780f-c935-4147-bf00-aa3ccb3dfcdc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_14cd780f-c935-4147-bf00-aa3ccb3dfcdc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_29c1ebba-1d9d-47fe-b169-e9b95c7f7fb1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_29c1ebba-1d9d-47fe-b169-e9b95c7f7fb1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_cb113e96-8193-4f76-9b3c-cf56491e84e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_cb113e96-8193-4f76-9b3c-cf56491e84e9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_1afb903c-43f5-4eef-96fa-3b231438bd32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d3960b43-d620-4f40-b0de-e522eda52a23" xlink:to="loc_us-gaap_Assets_1afb903c-43f5-4eef-96fa-3b231438bd32" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7389cd65-8478-4de3-b40c-959d7284448d" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_c68adeca-8b5f-46f3-afce-43b47c0517c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_AccountsPayableCurrent_c68adeca-8b5f-46f3-afce-43b47c0517c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_ff29142e-c7c0-434d-9a7e-5589943487b7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_ff29142e-c7c0-434d-9a7e-5589943487b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_1ddb7f53-5de4-4ef8-97d5-27c3157e5503" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_1ddb7f53-5de4-4ef8-97d5-27c3157e5503" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_31972730-ada8-41e9-a4ec-93957567f174" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_31972730-ada8-41e9-a4ec-93957567f174" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_c788edf4-6af5-4c4b-8269-124ef7332260" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_TaxesPayableCurrent_c788edf4-6af5-4c4b-8269-124ef7332260" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_25769b75-4d65-4d43-a54e-b1e4238db73c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_25769b75-4d65-4d43-a54e-b1e4238db73c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_819ee438-503c-4017-8627-7984725a1e93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_4c6b131d-be7d-4a2a-8e86-e4b2c7b6a5e4" xlink:to="loc_us-gaap_LiabilitiesCurrent_819ee438-503c-4017-8627-7984725a1e93" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent_9ef1eebd-ee1c-4d75-ae26-ae5c3fe4f978" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent_9ef1eebd-ee1c-4d75-ae26-ae5c3fe4f978" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_cbbeb3bc-2b6d-480a-b41d-bd2d8baf369d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_cbbeb3bc-2b6d-480a-b41d-bd2d8baf369d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_3dde772e-d3f1-4150-acc8-5718fd07e323" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_3dde772e-d3f1-4150-acc8-5718fd07e323" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_c59f7f7e-35ae-44e7-b4d6-2fc83124446e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_Liabilities_c59f7f7e-35ae-44e7-b4d6-2fc83124446e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_8f2715d0-37ad-4b8c-b4c6-b8d1bfaf78aa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_CommitmentsAndContingencies_8f2715d0-37ad-4b8c-b4c6-b8d1bfaf78aa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_7469e196-3949-4d5f-ae1b-692922f60b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_PreferredStockValue_7469e196-3949-4d5f-ae1b-692922f60b5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_59aeb72c-4f61-4024-be55-7d95f9c716fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_CommonStockValue_59aeb72c-4f61-4024-be55-7d95f9c716fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_b13da62f-8749-42bd-8e8a-3478ad96ed9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_AdditionalPaidInCapital_b13da62f-8749-42bd-8e8a-3478ad96ed9c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_4159d849-0c61-4908-93ea-e5110baa12f0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_4159d849-0c61-4908-93ea-e5110baa12f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue_94213a9b-9536-430f-af1c-d1d649c03a00" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_TreasuryStockValue_94213a9b-9536-430f-af1c-d1d649c03a00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_6e349246-c258-47d1-8110-11c38929caba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_6e349246-c258-47d1-8110-11c38929caba" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4f536119-ae67-4b1f-b3ea-f83fafe8ce7e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_d335e2a3-d456-4053-8192-4bce31c632b6" xlink:to="loc_us-gaap_StockholdersEquity_4f536119-ae67-4b1f-b3ea-f83fafe8ce7e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_7d0bc5a1-2bf8-48d6-9d14-83e98ee34d77" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_60b4687f-bfd8-4b4a-b9ea-ac0b28400714" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_7d0bc5a1-2bf8-48d6-9d14-83e98ee34d77" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_04cb8456-39b9-4bd1-ba0d-0f0f4532be5b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7389cd65-8478-4de3-b40c-959d7284448d" xlink:to="loc_us-gaap_StatementTable_04cb8456-39b9-4bd1-ba0d-0f0f4532be5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_04cb8456-39b9-4bd1-ba0d-0f0f4532be5b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc" xlink:to="loc_us-gaap_ClassOfStockDomain_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_06649f3f-7df6-4692-bbf3-763a25170be9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_4e7eb856-9717-43c0-b6a1-0d5276dd8fcc" xlink:to="loc_us-gaap_ClassOfStockDomain_06649f3f-7df6-4692-bbf3-763a25170be9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_1331f8f0-4f3b-42ce-84bb-d9dcec5f9e06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_06649f3f-7df6-4692-bbf3-763a25170be9" xlink:to="loc_us-gaap_CommonClassAMember_1331f8f0-4f3b-42ce-84bb-d9dcec5f9e06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_21344d59-1cd3-4174-93ca-6476bb96cd69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_06649f3f-7df6-4692-bbf3-763a25170be9" xlink:to="loc_us-gaap_CommonClassBMember_21344d59-1cd3-4174-93ca-6476bb96cd69" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="appf-20211231.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="iba8d9b4c03a74d2fadc9a656c88fa526_ConsolidatedBalanceSheetsParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_7fbc902a-5ed3-4ae8-889d-0835081a0317" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_7fbc902a-5ed3-4ae8-889d-0835081a0317" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_7afccd89-e954-4904-8b48-75446b898cb9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_7afccd89-e954-4904-8b48-75446b898cb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_60613d21-e6aa-46b8-9899-534c896fcd14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_PreferredStockSharesIssued_60613d21-e6aa-46b8-9899-534c896fcd14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_03bf23a7-0a69-4a49-a941-a30cc2f65445" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_03bf23a7-0a69-4a49-a941-a30cc2f65445" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_15626a85-3b98-45e9-a4ea-ae82f8a6aa63" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_15626a85-3b98-45e9-a4ea-ae82f8a6aa63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_352eda8c-1914-4ce6-be76-7427c1eedbfa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_352eda8c-1914-4ce6-be76-7427c1eedbfa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_37552ed1-c9d9-4c58-912e-def99a661f39" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_CommonStockSharesIssued_37552ed1-c9d9-4c58-912e-def99a661f39" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_0e64a0ed-f8d9-4168-9070-b38057a4b6ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_0e64a0ed-f8d9-4168-9070-b38057a4b6ce" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockShares_4d725dfb-9477-4227-84c3-7eda26ead0e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_TreasuryStockShares_4d725dfb-9477-4227-84c3-7eda26ead0e6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_ac00abcb-7994-4932-8b46-3b5aebf5eaed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c17c560e-4c6f-4f3f-a81a-0670ed3ce6ea" xlink:to="loc_us-gaap_StatementTable_ac00abcb-7994-4932-8b46-3b5aebf5eaed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_ac00abcb-7994-4932-8b46-3b5aebf5eaed" xlink:to="loc_us-gaap_StatementClassOfStockAxis_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11" xlink:to="loc_us-gaap_ClassOfStockDomain_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_50161cfc-6b61-4d70-9d96-104172247704" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0bcf7b5b-f2c6-4851-addc-6361c0f3aa11" xlink:to="loc_us-gaap_ClassOfStockDomain_50161cfc-6b61-4d70-9d96-104172247704" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_80300068-4188-4db1-9c12-ef9dff06edbb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50161cfc-6b61-4d70-9d96-104172247704" xlink:to="loc_us-gaap_CommonClassAMember_80300068-4188-4db1-9c12-ef9dff06edbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_50d0d114-0ae4-4b4a-83fd-6aea654a771e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_50161cfc-6b61-4d70-9d96-104172247704" xlink:to="loc_us-gaap_CommonClassBMember_50d0d114-0ae4-4b4a-83fd-6aea654a771e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="appf-20211231.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended" id="ia29bb3269ae342c78f0728870a2af3f9_ConsolidatedStatementsofStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_62cabb0e-b447-43f8-b8f5-a6b79e20bdad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_62cabb0e-b447-43f8-b8f5-a6b79e20bdad" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_d376d8c6-0654-47aa-9af5-ee8d85e3ae87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_SharesOutstanding_d376d8c6-0654-47aa-9af5-ee8d85e3ae87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_7445cd7a-f3cb-4db7-b060-de33cf4aeda6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockholdersEquity_7445cd7a-f3cb-4db7-b060-de33cf4aeda6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_abb0849b-1c79-4224-a01a-7880626a1b70" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_abb0849b-1c79-4224-a01a-7880626a1b70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_f6118762-c75e-48cc-9930-a725049a6c50" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_f6118762-c75e-48cc-9930-a725049a6c50" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_ed074891-b84c-437a-b240-db528e1dedbf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_ed074891-b84c-437a-b240-db528e1dedbf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsSharesIssuedNetOfSharesForTaxWithholdings_411ffd0e-d4c1-4ce5-9fab-ede5ea22d159" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsSharesIssuedNetOfSharesForTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_appf_RestrictedStockUnitsSharesIssuedNetOfSharesForTaxWithholdings_411ffd0e-d4c1-4ce5-9fab-ede5ea22d159" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsValueSharesIssuedNetOfTaxWithholdings_df2928f7-7ba2-48cf-8c19-aaca352a1b42" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsValueSharesIssuedNetOfTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_appf_RestrictedStockUnitsValueSharesIssuedNetOfTaxWithholdings_df2928f7-7ba2-48cf-8c19-aaca352a1b42" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions_0219eac3-00ee-41ac-8e00-7ca1d3d77919" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions_0219eac3-00ee-41ac-8e00-7ca1d3d77919" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_870c186c-cc4e-4061-8441-88b95c0e5801" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_870c186c-cc4e-4061-8441-88b95c0e5801" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockAmountConverted1_df21be2d-f2b7-4c0a-8ab0-3299e840be11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockAmountConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_ConversionOfStockAmountConverted1_df21be2d-f2b7-4c0a-8ab0-3299e840be11" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_1137e649-e0de-4bb0-93d1-a5a197e699ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_1137e649-e0de-4bb0-93d1-a5a197e699ec" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_0032a8da-995c-4494-9eb9-a9742106a21c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_0032a8da-995c-4494-9eb9-a9742106a21c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_5d57a726-ec77-47c3-8d3a-d6734102c1a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_5d57a726-ec77-47c3-8d3a-d6734102c1a2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_befbe0c2-82b9-474e-96f4-061094f38bf2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_befbe0c2-82b9-474e-96f4-061094f38bf2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_9f12ba58-47f2-404c-b7d2-65462c84b6be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_9f12ba58-47f2-404c-b7d2-65462c84b6be" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_3b475ad2-ba9d-457f-9cd6-efd8de1ac07e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_328736b7-1398-4a40-8411-747a7fc31ec2" xlink:to="loc_us-gaap_NetIncomeLoss_3b475ad2-ba9d-457f-9cd6-efd8de1ac07e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_a881e22a-be6b-46a5-81af-0b1b1dc758eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_97d77f0d-d2a4-4b31-b177-b7fcdf6bdb72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_638f0fc0-6da3-4890-aeb8-83cc305bbc51" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_62cabb0e-b447-43f8-b8f5-a6b79e20bdad" xlink:to="loc_us-gaap_StatementTable_638f0fc0-6da3-4890-aeb8-83cc305bbc51" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_854dbded-4563-430c-8983-9b724489e306" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_638f0fc0-6da3-4890-aeb8-83cc305bbc51" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_854dbded-4563-430c-8983-9b724489e306" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_854dbded-4563-430c-8983-9b724489e306_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_854dbded-4563-430c-8983-9b724489e306" xlink:to="loc_us-gaap_EquityComponentDomain_854dbded-4563-430c-8983-9b724489e306_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_854dbded-4563-430c-8983-9b724489e306" xlink:to="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_35b17ccc-1928-4f51-8bd4-f788280fe267" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:to="loc_us-gaap_CommonStockMember_35b17ccc-1928-4f51-8bd4-f788280fe267" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_0151c08c-b1f1-4383-a3fe-f2ab63f729ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_0151c08c-b1f1-4383-a3fe-f2ab63f729ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_cfdc6f84-7acd-4f95-8705-a7be4b76cf8d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_cfdc6f84-7acd-4f95-8705-a7be4b76cf8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_95392a19-7b9d-4901-80e4-4a1a290ad725" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:to="loc_us-gaap_TreasuryStockMember_95392a19-7b9d-4901-80e4-4a1a290ad725" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_1f41966d-6ebd-42d8-9cb1-1224acf36859" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ae4f1c1d-9009-4720-88ce-6ab577b6e3d7" xlink:to="loc_us-gaap_RetainedEarningsMember_1f41966d-6ebd-42d8-9cb1-1224acf36859" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_42c99461-f554-41c7-98a5-f39810c217c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_638f0fc0-6da3-4890-aeb8-83cc305bbc51" xlink:to="loc_us-gaap_StatementClassOfStockAxis_42c99461-f554-41c7-98a5-f39810c217c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_42c99461-f554-41c7-98a5-f39810c217c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_42c99461-f554-41c7-98a5-f39810c217c8" xlink:to="loc_us-gaap_ClassOfStockDomain_42c99461-f554-41c7-98a5-f39810c217c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9621d0c3-e362-484e-b0e2-02f3d6571135" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_42c99461-f554-41c7-98a5-f39810c217c8" xlink:to="loc_us-gaap_ClassOfStockDomain_9621d0c3-e362-484e-b0e2-02f3d6571135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_2e7117b4-9f0c-42d9-89ab-906c4edfd0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9621d0c3-e362-484e-b0e2-02f3d6571135" xlink:to="loc_us-gaap_CommonClassAMember_2e7117b4-9f0c-42d9-89ab-906c4edfd0d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_ecd2dda0-573d-4fe4-8fc6-78045b317ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9621d0c3-e362-484e-b0e2-02f3d6571135" xlink:to="loc_us-gaap_CommonClassBMember_ecd2dda0-573d-4fe4-8fc6-78045b317ef1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/SummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#SummaryofSignificantAccountingPoliciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/SummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="extended" id="i229dff5b27d24a01913aac825dce25d3_SummaryofSignificantAccountingPoliciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_0b683318-119f-4011-a009-be6ef8619f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_NumberOfOperatingSegments_0b683318-119f-4011-a009-be6ef8619f5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_f897210d-5953-4c2c-aac3-e9869b4d5b9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_NumberOfReportableSegments_f897210d-5953-4c2c-aac3-e9869b4d5b9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForOtherCreditLosses_a5cb99a4-0d5d-496b-b2ed-56e743c0bb99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProvisionForOtherCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_ProvisionForOtherCreditLosses_a5cb99a4-0d5d-496b-b2ed-56e743c0bb99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_90a40124-5a82-4ffd-9ba9-4e2c310a53a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_90a40124-5a82-4ffd-9ba9-4e2c310a53a7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLossNetOfTax_bca6d673-05cf-4f23-acf4-4398ed5b94ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GoodwillImpairmentLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_GoodwillImpairmentLossNetOfTax_bca6d673-05cf-4f23-acf4-4398ed5b94ea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_54466e6e-bd72-4d23-9c5d-b67bee2c04d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_54466e6e-bd72-4d23-9c5d-b67bee2c04d2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_ContractTermSubscriptionAgreement_c79b7a13-5ebe-4184-bc4e-ad11cb5b813b" xlink:href="appf-20211231.xsd#appf_ContractTermSubscriptionAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_appf_ContractTermSubscriptionAgreement_c79b7a13-5ebe-4184-bc4e-ad11cb5b813b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_f8371fbe-8a70-4ad7-b52e-9621819faba5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_f8371fbe-8a70-4ad7-b52e-9621819faba5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_d21171d9-83d5-417d-881c-a3544ce4f675" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_d21171d9-83d5-417d-881c-a3544ce4f675" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostNet_38facf35-153b-4f35-b3f6-b87d3fef4dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedContractCostNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_CapitalizedContractCostNet_38facf35-153b-4f35-b3f6-b87d3fef4dcf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostNetCurrent_983cef5d-4464-4af0-bd6b-799ea9245104" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedContractCostNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_CapitalizedContractCostNetCurrent_983cef5d-4464-4af0-bd6b-799ea9245104" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostNetNoncurrent_24a0e61e-6d27-45f4-97d9-667e04b17de7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedContractCostNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_CapitalizedContractCostNetNoncurrent_24a0e61e-6d27-45f4-97d9-667e04b17de7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortization_db9bc975-5dfd-47cf-97ed-0e60f1287203" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalizedContractCostAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_CapitalizedContractCostAmortization_db9bc975-5dfd-47cf-97ed-0e60f1287203" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_da9d94aa-c6c4-4b05-8b04-08759756b492" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_AdvertisingExpense_da9d94aa-c6c4-4b05-8b04-08759756b492" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_51d850e0-00f3-4d2b-9d90-a6aca0367bb0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_51d850e0-00f3-4d2b-9d90-a6aca0367bb0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_2511fd09-89de-4b65-bb64-a0017b3cb152" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5712444b-2882-4f1e-8184-a26d3b4db221" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5712444b-2882-4f1e-8184-a26d3b4db221" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5712444b-2882-4f1e-8184-a26d3b4db221_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5712444b-2882-4f1e-8184-a26d3b4db221" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5712444b-2882-4f1e-8184-a26d3b4db221_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c1910ec7-6302-41b7-8497-7dda9b1f1203" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5712444b-2882-4f1e-8184-a26d3b4db221" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c1910ec7-6302-41b7-8497-7dda9b1f1203" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ca18c80e-7bf3-4018-92cc-88a704dd2468" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c1910ec7-6302-41b7-8497-7dda9b1f1203" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ca18c80e-7bf3-4018-92cc-88a704dd2468" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ea3c9149-e9a0-406f-90de-974cdb86bfc0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:to="loc_srt_RangeAxis_ea3c9149-e9a0-406f-90de-974cdb86bfc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ea3c9149-e9a0-406f-90de-974cdb86bfc0_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ea3c9149-e9a0-406f-90de-974cdb86bfc0" xlink:to="loc_srt_RangeMember_ea3c9149-e9a0-406f-90de-974cdb86bfc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e14a3936-54de-4921-ba95-45546978d6e4" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ea3c9149-e9a0-406f-90de-974cdb86bfc0" xlink:to="loc_srt_RangeMember_e14a3936-54de-4921-ba95-45546978d6e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_797c2637-78ec-45be-9ad8-5d4d3a66f0bd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e14a3936-54de-4921-ba95-45546978d6e4" xlink:to="loc_srt_MinimumMember_797c2637-78ec-45be-9ad8-5d4d3a66f0bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_b6218dfb-ac14-47a1-94f4-b812c43f2367" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e14a3936-54de-4921-ba95-45546978d6e4" xlink:to="loc_srt_MaximumMember_b6218dfb-ac14-47a1-94f4-b812c43f2367" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:to="loc_us-gaap_AwardTypeAxis_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_213565cd-11e1-46fa-a128-b3856fa23f22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e5ca3350-171d-4a2e-a131-0f4d4cabd8f1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_213565cd-11e1-46fa-a128-b3856fa23f22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_bf47d2fe-b7b6-411d-bffb-fa3f9638ab6b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_213565cd-11e1-46fa-a128-b3856fa23f22" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_bf47d2fe-b7b6-411d-bffb-fa3f9638ab6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_18df3989-6130-45e6-8d56-edcde8b7ecc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e383ecc2-e2df-48ca-8cc5-b631c5d046b2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_18df3989-6130-45e6-8d56-edcde8b7ecc1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_18df3989-6130-45e6-8d56-edcde8b7ecc1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_18df3989-6130-45e6-8d56-edcde8b7ecc1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_18df3989-6130-45e6-8d56-edcde8b7ecc1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ad33a853-4946-465e-b548-6874f82027c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_18df3989-6130-45e6-8d56-edcde8b7ecc1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ad33a853-4946-465e-b548-6874f82027c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_41a34e3e-a179-4e13-a9a2-b1234f6be2d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ad33a853-4946-465e-b548-6874f82027c7" xlink:to="loc_us-gaap_PerformanceSharesMember_41a34e3e-a179-4e13-a9a2-b1234f6be2d1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails" xlink:type="extended" id="ie5795e2eda854df8becb3b53fbb7bf91_SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ddd211c6-2cce-4ca7-a1e0-9223c7b7e5df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_e5842477-7bc1-403d-a90d-9bacc516642e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ddd211c6-2cce-4ca7-a1e0-9223c7b7e5df" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_e5842477-7bc1-403d-a90d-9bacc516642e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9ecba805-bc55-480e-815e-3ec65535de13" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ddd211c6-2cce-4ca7-a1e0-9223c7b7e5df" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9ecba805-bc55-480e-815e-3ec65535de13" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_397ebad2-ee41-4f1c-b3cb-c24c454e053f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9ecba805-bc55-480e-815e-3ec65535de13" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_397ebad2-ee41-4f1c-b3cb-c24c454e053f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_397ebad2-ee41-4f1c-b3cb-c24c454e053f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_397ebad2-ee41-4f1c-b3cb-c24c454e053f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_397ebad2-ee41-4f1c-b3cb-c24c454e053f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_19a120ee-b6da-43e2-93ba-efd3fcff21df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_397ebad2-ee41-4f1c-b3cb-c24c454e053f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_19a120ee-b6da-43e2-93ba-efd3fcff21df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_da16e36e-1d08-4f06-81e9-ce3e4b5596a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_19a120ee-b6da-43e2-93ba-efd3fcff21df" xlink:to="loc_us-gaap_ComputerEquipmentMember_da16e36e-1d08-4f06-81e9-ce3e4b5596a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_1bad5cef-d8ab-4f5b-8eb4-3944dd667a3c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_19a120ee-b6da-43e2-93ba-efd3fcff21df" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_1bad5cef-d8ab-4f5b-8eb4-3944dd667a3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OfficeEquipmentMember_55399c86-9237-466e-a3d9-03e7291a3c27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_19a120ee-b6da-43e2-93ba-efd3fcff21df" xlink:to="loc_us-gaap_OfficeEquipmentMember_55399c86-9237-466e-a3d9-03e7291a3c27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_26ed14d8-47ab-4391-928d-8f4d909d1ebd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9ecba805-bc55-480e-815e-3ec65535de13" xlink:to="loc_srt_RangeAxis_26ed14d8-47ab-4391-928d-8f4d909d1ebd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_26ed14d8-47ab-4391-928d-8f4d909d1ebd_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_26ed14d8-47ab-4391-928d-8f4d909d1ebd" xlink:to="loc_srt_RangeMember_26ed14d8-47ab-4391-928d-8f4d909d1ebd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b08501b9-df6c-4bfb-93ae-ff299fb4e8c9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_26ed14d8-47ab-4391-928d-8f4d909d1ebd" xlink:to="loc_srt_RangeMember_b08501b9-df6c-4bfb-93ae-ff299fb4e8c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_af509789-6b58-44b4-bfb4-974463f2d4e0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b08501b9-df6c-4bfb-93ae-ff299fb4e8c9" xlink:to="loc_srt_MinimumMember_af509789-6b58-44b4-bfb4-974463f2d4e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a7f9ccd5-77e5-4f77-8e7d-79f972a80c90" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b08501b9-df6c-4bfb-93ae-ff299fb4e8c9" xlink:to="loc_srt_MaximumMember_a7f9ccd5-77e5-4f77-8e7d-79f972a80c90" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/DivestituresNarrativeDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#DivestituresNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/DivestituresNarrativeDetails" xlink:type="extended" id="i18f9bbaa19364c1baa729a1dadb19f08_DivestituresNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_f70fe59e-1532-4b2f-ac31-c6e6a8f6d956" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_f70fe59e-1532-4b2f-ac31-c6e6a8f6d956" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiaries_4c544e8a-99b8-4221-b4bc-924e266fec22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiaries_4c544e8a-99b8-4221-b4bc-924e266fec22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashOrPartNoncashDivestitureAmountOfConsiderationReceived1_c0e8afeb-d8ea-4818-8707-9de6466a1b2c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncashOrPartNoncashDivestitureAmountOfConsiderationReceived1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_NoncashOrPartNoncashDivestitureAmountOfConsiderationReceived1_c0e8afeb-d8ea-4818-8707-9de6466a1b2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashDivestedFromDeconsolidation_5a67ca6b-cbac-4ffe-9fb4-6bbcf4f59e97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashDivestedFromDeconsolidation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_CashDivestedFromDeconsolidation_5a67ca6b-cbac-4ffe-9fb4-6bbcf4f59e97" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustment_53d04841-9bcf-43ee-b13c-931d3505c962" xlink:href="appf-20211231.xsd#appf_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_appf_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustment_53d04841-9bcf-43ee-b13c-931d3505c962" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_DisposalGroupIncludingDiscontinuedOperationRetentionPeriod_3ab7bb39-9228-4f5d-b045-1d5799867478" xlink:href="appf-20211231.xsd#appf_DisposalGroupIncludingDiscontinuedOperationRetentionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_appf_DisposalGroupIncludingDiscontinuedOperationRetentionPeriod_3ab7bb39-9228-4f5d-b045-1d5799867478" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_c7910255-5789-4826-a6ae-66bcfeb65a88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_c7910255-5789-4826-a6ae-66bcfeb65a88" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_e923954d-9919-4b06-a7ba-13e108ed597f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_e923954d-9919-4b06-a7ba-13e108ed597f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_NoncashOrPartNoncashDivestitureAdjustmentToConsideration_5534d5f3-d923-4d7c-a3fa-6a906ffda99f" xlink:href="appf-20211231.xsd#appf_NoncashOrPartNoncashDivestitureAdjustmentToConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_appf_NoncashOrPartNoncashDivestitureAdjustmentToConsideration_5534d5f3-d923-4d7c-a3fa-6a906ffda99f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_DisposalGroupIncludingDiscontinuedOperationCapitalizedSoftware_60606850-89ee-415c-9446-198d93b24e1a" xlink:href="appf-20211231.xsd#appf_DisposalGroupIncludingDiscontinuedOperationCapitalizedSoftware"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_appf_DisposalGroupIncludingDiscontinuedOperationCapitalizedSoftware_60606850-89ee-415c-9446-198d93b24e1a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredRevenue_82eda2aa-db12-4d26-a856-a2e1fba7e721" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredRevenue_82eda2aa-db12-4d26-a856-a2e1fba7e721" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_22875e32-2d7e-4a33-aa80-7c6159f8f63f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_22875e32-2d7e-4a33-aa80-7c6159f8f63f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherIncome_382a3dfd-fc9d-4c25-b3e3-65069a1141cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherIncome_382a3dfd-fc9d-4c25-b3e3-65069a1141cc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b3212b69-2cf8-4d50-93b7-e6f7f4ad1020" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_36fc9940-4b69-4522-ae98-d65803246c33" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b3212b69-2cf8-4d50-93b7-e6f7f4ad1020" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_cc248636-1d62-4f69-bc3f-efb9dd558b59" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b3212b69-2cf8-4d50-93b7-e6f7f4ad1020" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_cc248636-1d62-4f69-bc3f-efb9dd558b59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_cc248636-1d62-4f69-bc3f-efb9dd558b59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_cc248636-1d62-4f69-bc3f-efb9dd558b59" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_cc248636-1d62-4f69-bc3f-efb9dd558b59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6aa178f6-60eb-4ab2-961c-d3662d95077e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_cc248636-1d62-4f69-bc3f-efb9dd558b59" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6aa178f6-60eb-4ab2-961c-d3662d95077e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_MyCaseMember_f7c42bd6-4b23-4f2e-90fa-1a3b27f402fb" xlink:href="appf-20211231.xsd#appf_MyCaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6aa178f6-60eb-4ab2-961c-d3662d95077e" xlink:to="loc_appf_MyCaseMember_f7c42bd6-4b23-4f2e-90fa-1a3b27f402fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_ef2ce856-803c-4c4b-87c5-fd25c096251a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b3212b69-2cf8-4d50-93b7-e6f7f4ad1020" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_ef2ce856-803c-4c4b-87c5-fd25c096251a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_ef2ce856-803c-4c4b-87c5-fd25c096251a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_ef2ce856-803c-4c4b-87c5-fd25c096251a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_ef2ce856-803c-4c4b-87c5-fd25c096251a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_887ffa48-9c8d-4f7a-85be-8e35571c6130" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_ef2ce856-803c-4c4b-87c5-fd25c096251a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_887ffa48-9c8d-4f7a-85be-8e35571c6130" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_62f7aa51-5f0c-4a69-b3b9-b3af636c636f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_887ffa48-9c8d-4f7a-85be-8e35571c6130" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_62f7aa51-5f0c-4a69-b3b9-b3af636c636f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsInvestmentSecuritiesDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#InvestmentsandFairValueMeasurementsInvestmentSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsInvestmentSecuritiesDetails" xlink:type="extended" id="i8de002de22b44999b18c25dc1ac0ec96_InvestmentsandFairValueMeasurementsInvestmentSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_9f009b2f-c52d-4c0e-bd27-9bf7709cbc18" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_9f009b2f-c52d-4c0e-bd27-9bf7709cbc18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_4d1cb6fb-9318-4073-bc1e-2a7cfb88a310" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_4d1cb6fb-9318-4073-bc1e-2a7cfb88a310" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_6326cdd7-02a5-4761-b2a5-15c9f08ef9c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_6326cdd7-02a5-4761-b2a5-15c9f08ef9c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_23580786-e1bf-4a9a-ab08-5afc30e912e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_23580786-e1bf-4a9a-ab08-5afc30e912e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_AvailableForSaleSecuritiesMaximumContractualMaturity_62a370eb-1750-4fe9-bc3f-4d38b55be572" xlink:href="appf-20211231.xsd#appf_AvailableForSaleSecuritiesMaximumContractualMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_appf_AvailableForSaleSecuritiesMaximumContractualMaturity_62a370eb-1750-4fe9-bc3f-4d38b55be572" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_ffbe3b50-43ca-4672-82bd-485d931a51ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_ffbe3b50-43ca-4672-82bd-485d931a51ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_7083c040-d979-455f-818e-371478f3c78f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_7083c040-d979-455f-818e-371478f3c78f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_01937d8b-63fe-4265-929d-0f66678db6c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_01937d8b-63fe-4265-929d-0f66678db6c6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_ad07b1d1-7ab4-4402-86c5-8b5832c56226" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_ad07b1d1-7ab4-4402-86c5-8b5832c56226" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1eff500a-f5c8-421a-b6e5-37ff04767f79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_67ebfe11-a69b-4d29-88ff-4225ad888183" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1eff500a-f5c8-421a-b6e5-37ff04767f79" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1eff500a-f5c8-421a-b6e5-37ff04767f79" xlink:to="loc_us-gaap_FinancialInstrumentAxis_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_243424ef-3ea5-41aa-92d0-30fae6a03b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_4e3c0a09-99cc-4ab2-9ed0-dd5eb505a44f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_243424ef-3ea5-41aa-92d0-30fae6a03b4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_3f0b2f40-9f91-4c00-8a4f-c46c857281de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_243424ef-3ea5-41aa-92d0-30fae6a03b4b" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_3f0b2f40-9f91-4c00-8a4f-c46c857281de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AgencySecuritiesMember_794925fe-dbf9-458c-85f0-abc4ddd4e00e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_243424ef-3ea5-41aa-92d0-30fae6a03b4b" xlink:to="loc_us-gaap_AgencySecuritiesMember_794925fe-dbf9-458c-85f0-abc4ddd4e00e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_f7aac743-d0a5-4d85-ba04-ad62550a5fbe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_243424ef-3ea5-41aa-92d0-30fae6a03b4b" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_f7aac743-d0a5-4d85-ba04-ad62550a5fbe" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsSalesandMaturitiesDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#InvestmentsandFairValueMeasurementsSalesandMaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsSalesandMaturitiesDetails" xlink:type="extended" id="i3db8569528854e11af28b6a3be674e81_InvestmentsandFairValueMeasurementsSalesandMaturitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_b740470b-7408-4f57-88fa-dc75b692a4a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_b740470b-7408-4f57-88fa-dc75b692a4a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_e859734a-4868-4a6c-bbb0-7de91bceada4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_e859734a-4868-4a6c-bbb0-7de91bceada4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_9afe29c1-58dd-4521-96c6-be872005df79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_9afe29c1-58dd-4521-96c6-be872005df79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_e19831c0-e956-4997-8340-3e08d04ac79a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_e19831c0-e956-4997-8340-3e08d04ac79a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_bdc9b2fd-b823-495b-8e9e-b8737c1324bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1eb63007-85db-41b0-96de-16bc8846f7a1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_bdc9b2fd-b823-495b-8e9e-b8737c1324bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_ffbc302c-c3bb-4b31-8e69-078022e5f167" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_bdc9b2fd-b823-495b-8e9e-b8737c1324bf" xlink:to="loc_us-gaap_FinancialInstrumentAxis_ffbc302c-c3bb-4b31-8e69-078022e5f167" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ffbc302c-c3bb-4b31-8e69-078022e5f167_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_ffbc302c-c3bb-4b31-8e69-078022e5f167" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ffbc302c-c3bb-4b31-8e69-078022e5f167_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f5bf9b8-a8e4-445e-a5ca-3b3d1cfa78de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_ffbc302c-c3bb-4b31-8e69-078022e5f167" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f5bf9b8-a8e4-445e-a5ca-3b3d1cfa78de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_4b7f64c3-5129-4c03-9265-3588436e1d02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f5bf9b8-a8e4-445e-a5ca-3b3d1cfa78de" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_4b7f64c3-5129-4c03-9265-3588436e1d02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AgencySecuritiesMember_c4425317-e54b-4b71-9c20-342801e8d31a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f5bf9b8-a8e4-445e-a5ca-3b3d1cfa78de" xlink:to="loc_us-gaap_AgencySecuritiesMember_c4425317-e54b-4b71-9c20-342801e8d31a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_64f1adcc-9434-46de-ac6f-66d7107df45c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f5bf9b8-a8e4-445e-a5ca-3b3d1cfa78de" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_64f1adcc-9434-46de-ac6f-66d7107df45c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsNarrativeDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#InvestmentsandFairValueMeasurementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsNarrativeDetails" xlink:type="extended" id="i39b1a42948824445a604db34fc688e7f_InvestmentsandFairValueMeasurementsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_66416fdf-6a0b-4c18-8474-998391a34776" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_51df0507-0285-4713-b070-d00b93a33242" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_66416fdf-6a0b-4c18-8474-998391a34776" xlink:to="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_51df0507-0285-4713-b070-d00b93a33242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_EquityMethodInvestmentRealizedGainFromRecoveryOfNoteReceivable_6e18f60a-42b1-4393-9d54-f244e63cf7be" xlink:href="appf-20211231.xsd#appf_EquityMethodInvestmentRealizedGainFromRecoveryOfNoteReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_66416fdf-6a0b-4c18-8474-998391a34776" xlink:to="loc_appf_EquityMethodInvestmentRealizedGainFromRecoveryOfNoteReceivable_6e18f60a-42b1-4393-9d54-f244e63cf7be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1c667c3b-a583-483e-b5d4-c60dd473324c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_66416fdf-6a0b-4c18-8474-998391a34776" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1c667c3b-a583-483e-b5d4-c60dd473324c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1c667c3b-a583-483e-b5d4-c60dd473324c" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_248ff885-ba58-4df9-9cc0-6812b6cca365" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_fb0caaee-9a24-4cdd-b50c-3bc4f77d5fca" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_248ff885-ba58-4df9-9cc0-6812b6cca365" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_SecureDocsMember_47a62a03-05d8-4b7d-a5fb-4f4fcc90f13a" xlink:href="appf-20211231.xsd#appf_SecureDocsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_248ff885-ba58-4df9-9cc0-6812b6cca365" xlink:to="loc_appf_SecureDocsMember_47a62a03-05d8-4b7d-a5fb-4f4fcc90f13a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_1e4006ca-3312-4146-a878-bd3647394149" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1c667c3b-a583-483e-b5d4-c60dd473324c" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_1e4006ca-3312-4146-a878-bd3647394149" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_1e4006ca-3312-4146-a878-bd3647394149_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1e4006ca-3312-4146-a878-bd3647394149" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_1e4006ca-3312-4146-a878-bd3647394149_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0d03a646-5842-4a3b-8cba-053a250bd285" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1e4006ca-3312-4146-a878-bd3647394149" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0d03a646-5842-4a3b-8cba-053a250bd285" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_a01e7ea8-3c13-4533-8cb2-376a3c5e7680" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_0d03a646-5842-4a3b-8cba-053a250bd285" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_a01e7ea8-3c13-4533-8cb2-376a3c5e7680" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsFairValueMeasurementsDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#InvestmentsandFairValueMeasurementsFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/InvestmentsandFairValueMeasurementsFairValueMeasurementsDetails" xlink:type="extended" id="i18b28cc9dda747faa1e0a3e385d652de_InvestmentsandFairValueMeasurementsFairValueMeasurementsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c3fdeb3f-b679-4521-82f4-87a58e40b658" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_d65eb3b5-135a-4afb-88c8-6eb36dd4feed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c3fdeb3f-b679-4521-82f4-87a58e40b658" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_d65eb3b5-135a-4afb-88c8-6eb36dd4feed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_cf131174-1893-413f-a621-6cef0f454e23" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c3fdeb3f-b679-4521-82f4-87a58e40b658" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_cf131174-1893-413f-a621-6cef0f454e23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_116a8e88-ca51-48c3-9c22-f383f8c2d3a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c3fdeb3f-b679-4521-82f4-87a58e40b658" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_116a8e88-ca51-48c3-9c22-f383f8c2d3a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c3fdeb3f-b679-4521-82f4-87a58e40b658" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_2544c14c-f03f-4471-8aab-df095c315c22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_2544c14c-f03f-4471-8aab-df095c315c22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_2544c14c-f03f-4471-8aab-df095c315c22_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_2544c14c-f03f-4471-8aab-df095c315c22" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_2544c14c-f03f-4471-8aab-df095c315c22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_7a7301f7-b8ee-4b68-b20a-dd1de1ffacea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_2544c14c-f03f-4471-8aab-df095c315c22" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_7a7301f7-b8ee-4b68-b20a-dd1de1ffacea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_32b186aa-1bea-4ebb-93a9-3f8ecb2b5445" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_7a7301f7-b8ee-4b68-b20a-dd1de1ffacea" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_32b186aa-1bea-4ebb-93a9-3f8ecb2b5445" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f52a08e1-dd02-46e8-aeed-fc119199705d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f52a08e1-dd02-46e8-aeed-fc119199705d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f52a08e1-dd02-46e8-aeed-fc119199705d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f52a08e1-dd02-46e8-aeed-fc119199705d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f52a08e1-dd02-46e8-aeed-fc119199705d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f7fdbd77-e839-43c4-b245-5f6cb5b4613c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f52a08e1-dd02-46e8-aeed-fc119199705d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f7fdbd77-e839-43c4-b245-5f6cb5b4613c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_ad29598b-f2ec-40db-9d29-80e8f48d5c79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f7fdbd77-e839-43c4-b245-5f6cb5b4613c" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_ad29598b-f2ec-40db-9d29-80e8f48d5c79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_fda373e1-aa6e-4013-9189-0fa381e5bac6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f7fdbd77-e839-43c4-b245-5f6cb5b4613c" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_fda373e1-aa6e-4013-9189-0fa381e5bac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_de2e0fdb-3af6-4a7b-a937-724cca84935b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f7fdbd77-e839-43c4-b245-5f6cb5b4613c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_de2e0fdb-3af6-4a7b-a937-724cca84935b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_7eec8ccb-54fb-4ea4-902b-fe471e955d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_7eec8ccb-54fb-4ea4-902b-fe471e955d3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_7eec8ccb-54fb-4ea4-902b-fe471e955d3d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_7eec8ccb-54fb-4ea4-902b-fe471e955d3d" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_7eec8ccb-54fb-4ea4-902b-fe471e955d3d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_475e42d7-8b57-4e2e-a9f8-870d6756c33d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_7eec8ccb-54fb-4ea4-902b-fe471e955d3d" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_475e42d7-8b57-4e2e-a9f8-870d6756c33d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_8a0eed77-f381-4444-b998-0a88a1ec7226" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_475e42d7-8b57-4e2e-a9f8-870d6756c33d" xlink:to="loc_us-gaap_MoneyMarketFundsMember_8a0eed77-f381-4444-b998-0a88a1ec7226" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_0f91c864-e063-4df9-92d1-8845f4e7c25b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_475e42d7-8b57-4e2e-a9f8-870d6756c33d" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_0f91c864-e063-4df9-92d1-8845f4e7c25b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_cebdd256-871d-48f2-a8f4-7d45e18b362a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7066360d-eb3e-4ad8-a9b6-8f3be4b90354" xlink:to="loc_us-gaap_FinancialInstrumentAxis_cebdd256-871d-48f2-a8f4-7d45e18b362a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_cebdd256-871d-48f2-a8f4-7d45e18b362a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_cebdd256-871d-48f2-a8f4-7d45e18b362a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_cebdd256-871d-48f2-a8f4-7d45e18b362a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1ee4f09f-e732-4dbc-a6af-9824a980c394" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_cebdd256-871d-48f2-a8f4-7d45e18b362a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1ee4f09f-e732-4dbc-a6af-9824a980c394" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_03b1d692-6bac-4a66-a716-172b418a987c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1ee4f09f-e732-4dbc-a6af-9824a980c394" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_03b1d692-6bac-4a66-a716-172b418a987c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AgencySecuritiesMember_181db672-27e3-4e92-8f9c-1c068722777d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1ee4f09f-e732-4dbc-a6af-9824a980c394" xlink:to="loc_us-gaap_AgencySecuritiesMember_181db672-27e3-4e92-8f9c-1c068722777d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_35777b36-d777-462c-9023-e91a89834c98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1ee4f09f-e732-4dbc-a6af-9824a980c394" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_35777b36-d777-462c-9023-e91a89834c98" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/PropertyandEquipmentnetDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#PropertyandEquipmentnetDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/PropertyandEquipmentnetDetails" xlink:type="extended" id="id5e78fceb43b4485a235cf83de33d264_PropertyandEquipmentnetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_6fc1bae7-55dd-4967-8b99-55c4074d02ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_6fc1bae7-55dd-4967-8b99-55c4074d02ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4ef25675-5228-4d9f-9a78-0c79bd694857" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4ef25675-5228-4d9f-9a78-0c79bd694857" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_777372d5-7bdd-4beb-a5e9-e5f71594b178" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_777372d5-7bdd-4beb-a5e9-e5f71594b178" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_92b321e7-f0d4-43c6-a102-5b792aef301a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:to="loc_us-gaap_Depreciation_92b321e7-f0d4-43c6-a102-5b792aef301a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1034de15-0209-44ff-8095-e2e9fb56fdbd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_de2ffd6b-b766-478a-b6a5-2307c2e8dcac" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1034de15-0209-44ff-8095-e2e9fb56fdbd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1034de15-0209-44ff-8095-e2e9fb56fdbd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b5379099-f6e6-4e1d-9850-6d4c6f9afbc5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_cf2de86b-c546-45b3-8d86-a1d4f397a08c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:to="loc_us-gaap_ComputerEquipmentMember_cf2de86b-c546-45b3-8d86-a1d4f397a08c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_3c4207f2-5dce-4597-9fbb-eeaeac0bfec4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_3c4207f2-5dce-4597-9fbb-eeaeac0bfec4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OfficeEquipmentMember_53688222-576e-4093-af2a-a71fc8978623" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:to="loc_us-gaap_OfficeEquipmentMember_53688222-576e-4093-af2a-a71fc8978623" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_d954e1fb-9111-4650-8f58-8dcf154d185e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_d954e1fb-9111-4650-8f58-8dcf154d185e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_680bb526-c5da-4cc1-8dda-3d6ff68200dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_57b9f438-7bcc-481e-bb23-a816adfdbb30" xlink:to="loc_us-gaap_ConstructionInProgressMember_680bb526-c5da-4cc1-8dda-3d6ff68200dd" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/IntangibleAssetsnetFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#IntangibleAssetsnetFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/IntangibleAssetsnetFiniteLivedIntangibleAssetsDetails" xlink:type="extended" id="i831bcab53ac24b8295cfe6a1e03ad1b7_IntangibleAssetsnetFiniteLivedIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_f97f86b7-fe6f-493f-adab-3976677420d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_f97f86b7-fe6f-493f-adab-3976677420d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_06918c8c-b691-44b1-9e3d-ae214dfab2f8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_06918c8c-b691-44b1-9e3d-ae214dfab2f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d03bd3fd-2589-418d-bbe6-eff58c255806" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d03bd3fd-2589-418d-bbe6-eff58c255806" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e351d4f0-e42e-4bad-b961-3d6616f87bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e351d4f0-e42e-4bad-b961-3d6616f87bd2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5c66445-ef5f-475a-84da-b8e2d7a447fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_600888a4-b4e9-4c1f-b816-2dab2f899f18" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5c66445-ef5f-475a-84da-b8e2d7a447fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_12c45770-6d3c-4e91-815a-b6d5c3eff3ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5c66445-ef5f-475a-84da-b8e2d7a447fa" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_12c45770-6d3c-4e91-815a-b6d5c3eff3ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_12c45770-6d3c-4e91-815a-b6d5c3eff3ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_12c45770-6d3c-4e91-815a-b6d5c3eff3ba" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_12c45770-6d3c-4e91-815a-b6d5c3eff3ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_12c45770-6d3c-4e91-815a-b6d5c3eff3ba" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_eca5b952-c426-406d-b6ea-2d95c8fb6ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_us-gaap_CustomerRelationshipsMember_eca5b952-c426-406d-b6ea-2d95c8fb6ab3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_DatabaseMember_cc0f5120-d740-4253-8ed1-8e1a850ce103" xlink:href="appf-20211231.xsd#appf_DatabaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_appf_DatabaseMember_cc0f5120-d740-4253-8ed1-8e1a850ce103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_TechnologyMember_5f7d014c-cd66-48c9-8387-3714b0304013" xlink:href="appf-20211231.xsd#appf_TechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_appf_TechnologyMember_5f7d014c-cd66-48c9-8387-3714b0304013" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_bebcf190-6cfe-4cdc-9742-510056b8fbd0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_bebcf190-6cfe-4cdc-9742-510056b8fbd0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_PartnerRelationshipsMember_d6d657ab-7be6-4c39-9b08-9715c46c8850" xlink:href="appf-20211231.xsd#appf_PartnerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_appf_PartnerRelationshipsMember_d6d657ab-7be6-4c39-9b08-9715c46c8850" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_b9c518d0-bfc2-4f5a-9b98-c9d95bfc6837" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_b9c518d0-bfc2-4f5a-9b98-c9d95bfc6837" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternetDomainNamesMember_ce57a8c0-bd34-4876-b27c-35ee0a82351d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InternetDomainNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_us-gaap_InternetDomainNamesMember_ce57a8c0-bd34-4876-b27c-35ee0a82351d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_8a02ce17-7f73-4386-b6f3-ddd06c0c0b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c17c9b87-f2da-4f8e-942f-3c1691d733ee" xlink:to="loc_us-gaap_PatentsMember_8a02ce17-7f73-4386-b6f3-ddd06c0c0b5e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_8048b37c-0b7f-4a5a-8446-8b7e5933ae31" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5c66445-ef5f-475a-84da-b8e2d7a447fa" xlink:to="loc_srt_RangeAxis_8048b37c-0b7f-4a5a-8446-8b7e5933ae31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8048b37c-0b7f-4a5a-8446-8b7e5933ae31_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_8048b37c-0b7f-4a5a-8446-8b7e5933ae31" xlink:to="loc_srt_RangeMember_8048b37c-0b7f-4a5a-8446-8b7e5933ae31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_04c0e1b2-0b4f-4d93-b366-277f4449f100" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_8048b37c-0b7f-4a5a-8446-8b7e5933ae31" xlink:to="loc_srt_RangeMember_04c0e1b2-0b4f-4d93-b366-277f4449f100" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_53ffbda1-99eb-4d8d-a7b0-4afc780cf990" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_04c0e1b2-0b4f-4d93-b366-277f4449f100" xlink:to="loc_srt_WeightedAverageMember_53ffbda1-99eb-4d8d-a7b0-4afc780cf990" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/LeasesNarrativeDetails" xlink:type="extended" id="ic30f6e0c0ff44adaacc72deecb215aad_LeasesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_6d745606-ded6-457d-a3c6-58707fd1c7e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_2b8b317c-d001-4d6d-bbe3-b1fd3d2af00d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6d745606-ded6-457d-a3c6-58707fd1c7e5" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_2b8b317c-d001-4d6d-bbe3-b1fd3d2af00d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseRenewalTerm_e41f52e3-9c60-4c1f-9b3f-e571870e6363" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6d745606-ded6-457d-a3c6-58707fd1c7e5" xlink:to="loc_us-gaap_LessorOperatingLeaseRenewalTerm_e41f52e3-9c60-4c1f-9b3f-e571870e6363" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_cbebca64-a02e-43aa-9720-84c2b0e73c1d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6d745606-ded6-457d-a3c6-58707fd1c7e5" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_cbebca64-a02e-43aa-9720-84c2b0e73c1d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_81aed8b0-9a2d-458f-a126-46627fed8777" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_cbebca64-a02e-43aa-9720-84c2b0e73c1d" xlink:to="loc_srt_RangeAxis_81aed8b0-9a2d-458f-a126-46627fed8777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_81aed8b0-9a2d-458f-a126-46627fed8777_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_81aed8b0-9a2d-458f-a126-46627fed8777" xlink:to="loc_srt_RangeMember_81aed8b0-9a2d-458f-a126-46627fed8777_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_dfb618d3-a87b-44ae-8a97-ab7a798ed84c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_81aed8b0-9a2d-458f-a126-46627fed8777" xlink:to="loc_srt_RangeMember_dfb618d3-a87b-44ae-8a97-ab7a798ed84c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4be97dbd-1a58-4c4d-beb9-32f7156ff2a1" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_dfb618d3-a87b-44ae-8a97-ab7a798ed84c" xlink:to="loc_srt_MinimumMember_4be97dbd-1a58-4c4d-beb9-32f7156ff2a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a6e96275-48c0-4492-b770-79c7179e6e27" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_dfb618d3-a87b-44ae-8a97-ab7a798ed84c" xlink:to="loc_srt_MaximumMember_a6e96275-48c0-4492-b770-79c7179e6e27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#CommitmentsandContingenciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="extended" id="i92cadce3a65b4e3583fd0e4ecdebad8a_CommitmentsandContingenciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_PropertyLiabilityAndCasualtyInsurancePerIncidentAndPerResidenceCoverageLimit_dc6ffd0e-c48e-4052-8184-9477decb832a" xlink:href="appf-20211231.xsd#appf_PropertyLiabilityAndCasualtyInsurancePerIncidentAndPerResidenceCoverageLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:to="loc_appf_PropertyLiabilityAndCasualtyInsurancePerIncidentAndPerResidenceCoverageLimit_dc6ffd0e-c48e-4052-8184-9477decb832a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_6698bfc3-79fd-414a-8dbd-94c84437fd32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_6698bfc3-79fd-414a-8dbd-94c84437fd32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpensePropertyCasualtyLiability_0ab47f89-a568-4ec5-8215-80ea9c5a9393" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpensePropertyCasualtyLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpensePropertyCasualtyLiability_0ab47f89-a568-4ec5-8215-80ea9c5a9393" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_PropertyLiabilityAndCasualtyInsuranceDepositsHeldWithThirdPartyAsCollateralForServices_56677993-9c67-47aa-a2ab-509c3ceb40bb" xlink:href="appf-20211231.xsd#appf_PropertyLiabilityAndCasualtyInsuranceDepositsHeldWithThirdPartyAsCollateralForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:to="loc_appf_PropertyLiabilityAndCasualtyInsuranceDepositsHeldWithThirdPartyAsCollateralForServices_56677993-9c67-47aa-a2ab-509c3ceb40bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_2d8f4646-20dc-46f6-bc9d-05348b6378d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_b432f6b8-4fa3-49e1-a20d-348cbb10664f" xlink:to="loc_us-gaap_LossContingenciesTable_2d8f4646-20dc-46f6-bc9d-05348b6378d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_1d514e7b-a1e8-480a-9b6b-97fc3db079a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_2d8f4646-20dc-46f6-bc9d-05348b6378d1" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_1d514e7b-a1e8-480a-9b6b-97fc3db079a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_1d514e7b-a1e8-480a-9b6b-97fc3db079a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_1d514e7b-a1e8-480a-9b6b-97fc3db079a3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_1d514e7b-a1e8-480a-9b6b-97fc3db079a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_3b6279f5-74da-49c8-8ec8-81a1a8a0507d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_1d514e7b-a1e8-480a-9b6b-97fc3db079a3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_3b6279f5-74da-49c8-8ec8-81a1a8a0507d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_ffc2dfde-56d0-47de-9fdb-1e03fbec461b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_3b6279f5-74da-49c8-8ec8-81a1a8a0507d" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_ffc2dfde-56d0-47de-9fdb-1e03fbec461b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_69cc97c3-a5a2-4666-b462-5176e0f63571" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_3b6279f5-74da-49c8-8ec8-81a1a8a0507d" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_69cc97c3-a5a2-4666-b462-5176e0f63571" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockholdersEquityAmendedandRestatedCertificateofIncorporationDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockholdersEquityAmendedandRestatedCertificateofIncorporationDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockholdersEquityAmendedandRestatedCertificateofIncorporationDetails" xlink:type="extended" id="ib9f33774a08a44dbab9d8013d0458466_StockholdersEquityAmendedandRestatedCertificateofIncorporationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalUnitsAuthorized_6dd5722d-8947-41ca-9192-85c32a97ceb6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalUnitsAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:to="loc_us-gaap_CapitalUnitsAuthorized_6dd5722d-8947-41ca-9192-85c32a97ceb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_40a3570c-4615-4641-8a1c-b853204c1302" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_40a3570c-4615-4641-8a1c-b853204c1302" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_80db7a1c-9356-4dfb-a302-865f4c4dde79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_80db7a1c-9356-4dfb-a302-865f4c4dde79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_f0435004-583b-486b-b6cc-68b8c37c0a16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_f0435004-583b-486b-b6cc-68b8c37c0a16" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_a92492aa-e617-4ecd-b8eb-3b41e928e9de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_315446c8-da95-4837-be37-0a0f967d738d" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_a92492aa-e617-4ecd-b8eb-3b41e928e9de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_43a120e3-8c3b-4d9d-ab9f-212ff49ac496" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_a92492aa-e617-4ecd-b8eb-3b41e928e9de" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_43a120e3-8c3b-4d9d-ab9f-212ff49ac496" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_43a120e3-8c3b-4d9d-ab9f-212ff49ac496_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_43a120e3-8c3b-4d9d-ab9f-212ff49ac496" xlink:to="loc_us-gaap_EquityComponentDomain_43a120e3-8c3b-4d9d-ab9f-212ff49ac496_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_642cc4fa-93e6-4ec3-9038-1952cba54c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_43a120e3-8c3b-4d9d-ab9f-212ff49ac496" xlink:to="loc_us-gaap_EquityComponentDomain_642cc4fa-93e6-4ec3-9038-1952cba54c1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_722a6122-81f8-4bb4-9c68-d522ff2e6791" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_642cc4fa-93e6-4ec3-9038-1952cba54c1b" xlink:to="loc_us-gaap_CommonStockMember_722a6122-81f8-4bb4-9c68-d522ff2e6791" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_91bbc663-5e6f-4e2d-ad17-c09c8ea7b374" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_642cc4fa-93e6-4ec3-9038-1952cba54c1b" xlink:to="loc_us-gaap_PreferredStockMember_91bbc663-5e6f-4e2d-ad17-c09c8ea7b374" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_912701fe-42f0-4447-b155-9beb3faa7b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_a92492aa-e617-4ecd-b8eb-3b41e928e9de" xlink:to="loc_us-gaap_StatementClassOfStockAxis_912701fe-42f0-4447-b155-9beb3faa7b7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_912701fe-42f0-4447-b155-9beb3faa7b7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_912701fe-42f0-4447-b155-9beb3faa7b7c" xlink:to="loc_us-gaap_ClassOfStockDomain_912701fe-42f0-4447-b155-9beb3faa7b7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7622e75d-9056-47c6-b8c1-a445ce3aa873" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_912701fe-42f0-4447-b155-9beb3faa7b7c" xlink:to="loc_us-gaap_ClassOfStockDomain_7622e75d-9056-47c6-b8c1-a445ce3aa873" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_8136fcda-277b-4446-a26a-04f575a06697" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7622e75d-9056-47c6-b8c1-a445ce3aa873" xlink:to="loc_us-gaap_CommonClassAMember_8136fcda-277b-4446-a26a-04f575a06697" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_7be47cfc-1450-46e7-a38a-6396fb29f7da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7622e75d-9056-47c6-b8c1-a445ce3aa873" xlink:to="loc_us-gaap_CommonClassBMember_7be47cfc-1450-46e7-a38a-6396fb29f7da" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockholdersEquityClassACommonStockandClassBCommonStockReverseStockSplitDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockholdersEquityClassACommonStockandClassBCommonStockReverseStockSplitDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockholdersEquityClassACommonStockandClassBCommonStockReverseStockSplitDetails" xlink:type="extended" id="ifdfe78538fab4032a7ca373f7aab691e_StockholdersEquityClassACommonStockandClassBCommonStockReverseStockSplitDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_CommonStockNumberOfVotesPerShare_bf011b56-32e5-47c3-ac5e-30cdd4751475" xlink:href="appf-20211231.xsd#appf_CommonStockNumberOfVotesPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:to="loc_appf_CommonStockNumberOfVotesPerShare_bf011b56-32e5-47c3-ac5e-30cdd4751475" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_ConversionOfStockNumberOfSharesIssuableUponConversion_660cbf90-5295-4344-8cbe-f4fb2257ae40" xlink:href="appf-20211231.xsd#appf_ConversionOfStockNumberOfSharesIssuableUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:to="loc_appf_ConversionOfStockNumberOfSharesIssuableUponConversion_660cbf90-5295-4344-8cbe-f4fb2257ae40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_ConversionOfStockNumberOfSharesIssuableUponConversionDueToTransfer_d396c75f-3fd0-4266-921a-1ba938d2de00" xlink:href="appf-20211231.xsd#appf_ConversionOfStockNumberOfSharesIssuableUponConversionDueToTransfer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:to="loc_appf_ConversionOfStockNumberOfSharesIssuableUponConversionDueToTransfer_d396c75f-3fd0-4266-921a-1ba938d2de00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_CommonStockAutomaticConversionThreshold_93bbda6e-a4d7-435d-866d-36105b84c560" xlink:href="appf-20211231.xsd#appf_CommonStockAutomaticConversionThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:to="loc_appf_CommonStockAutomaticConversionThreshold_93bbda6e-a4d7-435d-866d-36105b84c560" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_32bf7608-ddba-4e7e-aca6-c0bc976a74dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_bb91b54d-0e21-45d0-a9cf-1c8598a99f5a" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_32bf7608-ddba-4e7e-aca6-c0bc976a74dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_478defd2-76e6-458d-953e-915182465030" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_32bf7608-ddba-4e7e-aca6-c0bc976a74dc" xlink:to="loc_us-gaap_StatementClassOfStockAxis_478defd2-76e6-458d-953e-915182465030" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_478defd2-76e6-458d-953e-915182465030_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_478defd2-76e6-458d-953e-915182465030" xlink:to="loc_us-gaap_ClassOfStockDomain_478defd2-76e6-458d-953e-915182465030_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9bbfa353-46f5-4402-b41c-ddc01b1c9a9a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_478defd2-76e6-458d-953e-915182465030" xlink:to="loc_us-gaap_ClassOfStockDomain_9bbfa353-46f5-4402-b41c-ddc01b1c9a9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_6c7bca36-bc7a-4d48-b1cd-b0247e72b0db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9bbfa353-46f5-4402-b41c-ddc01b1c9a9a" xlink:to="loc_us-gaap_CommonClassAMember_6c7bca36-bc7a-4d48-b1cd-b0247e72b0db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_d56ac730-71c7-42ed-b347-1492fb797924" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9bbfa353-46f5-4402-b41c-ddc01b1c9a9a" xlink:to="loc_us-gaap_CommonClassBMember_d56ac730-71c7-42ed-b347-1492fb797924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_71977ae3-547a-41fe-b4ab-64edaabbd85c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_32bf7608-ddba-4e7e-aca6-c0bc976a74dc" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_71977ae3-547a-41fe-b4ab-64edaabbd85c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_71977ae3-547a-41fe-b4ab-64edaabbd85c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_71977ae3-547a-41fe-b4ab-64edaabbd85c" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_71977ae3-547a-41fe-b4ab-64edaabbd85c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_c9427dc2-0beb-411b-a01e-e12c7ca389db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_71977ae3-547a-41fe-b4ab-64edaabbd85c" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_c9427dc2-0beb-411b-a01e-e12c7ca389db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_CommonClassBToCommonClassAMember_a953db7b-8fa1-48d5-86c4-da71cef9a8ce" xlink:href="appf-20211231.xsd#appf_CommonClassBToCommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_c9427dc2-0beb-411b-a01e-e12c7ca389db" xlink:to="loc_appf_CommonClassBToCommonClassAMember_a953db7b-8fa1-48d5-86c4-da71cef9a8ce" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockBasedCompensationStockOptionPlansDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockBasedCompensationStockOptionPlansDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockBasedCompensationStockOptionPlansDetails" xlink:type="extended" id="i66624e0606f449269ed5eb37e72b2325_StockBasedCompensationStockOptionPlansDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualCommonStockReservedForFutureIssuance_e083f269-123f-48c7-9b70-475d02a5d641" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualCommonStockReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualCommonStockReservedForFutureIssuance_e083f269-123f-48c7-9b70-475d02a5d641" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_0336803a-ea13-4374-880f-c30954e9715d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_0336803a-ea13-4374-880f-c30954e9715d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_1b00f76f-3aa4-4041-ab9d-22bb06cd1005" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_1b00f76f-3aa4-4041-ab9d-22bb06cd1005" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_51cc5e43-ee2f-4dbf-b2e4-a51a4ddbd68a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_51cc5e43-ee2f-4dbf-b2e4-a51a4ddbd68a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_e0e8618e-f056-43b1-911f-a9193afacc4c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_e0e8618e-f056-43b1-911f-a9193afacc4c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_03d5f63b-689e-4036-bce7-a054ebb578d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_66846b92-d438-4735-a227-e8c453acd8c6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_03d5f63b-689e-4036-bce7-a054ebb578d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e5b3a2a0-2357-4774-895f-d831dfbc9cfb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_03d5f63b-689e-4036-bce7-a054ebb578d1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e5b3a2a0-2357-4774-895f-d831dfbc9cfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e5b3a2a0-2357-4774-895f-d831dfbc9cfb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e5b3a2a0-2357-4774-895f-d831dfbc9cfb" xlink:to="loc_us-gaap_ClassOfStockDomain_e5b3a2a0-2357-4774-895f-d831dfbc9cfb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ceb71906-fa3d-4b09-97d2-8937c7d16353" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e5b3a2a0-2357-4774-895f-d831dfbc9cfb" xlink:to="loc_us-gaap_ClassOfStockDomain_ceb71906-fa3d-4b09-97d2-8937c7d16353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_8908dea3-acd5-4a9e-bf90-8d9eca94e995" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ceb71906-fa3d-4b09-97d2-8937c7d16353" xlink:to="loc_us-gaap_CommonClassAMember_8908dea3-acd5-4a9e-bf90-8d9eca94e995" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_710fbc78-dd54-4fbc-ae11-bf5423d7254f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_03d5f63b-689e-4036-bce7-a054ebb578d1" xlink:to="loc_us-gaap_PlanNameAxis_710fbc78-dd54-4fbc-ae11-bf5423d7254f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_710fbc78-dd54-4fbc-ae11-bf5423d7254f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_710fbc78-dd54-4fbc-ae11-bf5423d7254f" xlink:to="loc_us-gaap_PlanNameDomain_710fbc78-dd54-4fbc-ae11-bf5423d7254f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_1104ebe2-e580-4af2-8825-062f6289b0ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_710fbc78-dd54-4fbc-ae11-bf5423d7254f" xlink:to="loc_us-gaap_PlanNameDomain_1104ebe2-e580-4af2-8825-062f6289b0ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_TwoThousandFifteenStockIncentivePlanMember_a82e00d3-cddf-493b-b903-f64d0e094c48" xlink:href="appf-20211231.xsd#appf_TwoThousandFifteenStockIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_1104ebe2-e580-4af2-8825-062f6289b0ac" xlink:to="loc_appf_TwoThousandFifteenStockIncentivePlanMember_a82e00d3-cddf-493b-b903-f64d0e094c48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_317e6002-d6c9-48ba-b9e8-80bbdb608ba6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_03d5f63b-689e-4036-bce7-a054ebb578d1" xlink:to="loc_us-gaap_AwardTypeAxis_317e6002-d6c9-48ba-b9e8-80bbdb608ba6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_317e6002-d6c9-48ba-b9e8-80bbdb608ba6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_317e6002-d6c9-48ba-b9e8-80bbdb608ba6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_317e6002-d6c9-48ba-b9e8-80bbdb608ba6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19b5a8e7-805a-4905-a5bb-1ef868bed2a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_317e6002-d6c9-48ba-b9e8-80bbdb608ba6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19b5a8e7-805a-4905-a5bb-1ef868bed2a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4197e6bd-c32c-49e8-941d-1b6d3dd91c88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19b5a8e7-805a-4905-a5bb-1ef868bed2a8" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4197e6bd-c32c-49e8-941d-1b6d3dd91c88" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockBasedCompensationRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockUnitsDetails" xlink:type="extended" id="i48f622f3171a40c78ee5529699827ed1_StockBasedCompensationRestrictedStockUnitsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_074a70cd-a124-4f59-ba49-f9d3030efdb7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_074a70cd-a124-4f59-ba49-f9d3030efdb7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_ed25684f-a230-4793-8f96-ec50f91a6a6b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_ed25684f-a230-4793-8f96-ec50f91a6a6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a6324b50-79d8-4c49-8240-8291c14ca14c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a6324b50-79d8-4c49-8240-8291c14ca14c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_f8eeabb7-4843-49ca-aa17-e54f0aae0222" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_f8eeabb7-4843-49ca-aa17-e54f0aae0222" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_639d16da-f0d9-47f5-9009-10140bffc894" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b82c43d7-9e5c-4cab-be0e-28a553a6958c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_639d16da-f0d9-47f5-9009-10140bffc894" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_0bf2648b-226f-4d1b-aac8-c7d302a170d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_074a70cd-a124-4f59-ba49-f9d3030efdb7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5d8277ce-1442-4ea6-9a05-2577949d92cd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5d8277ce-1442-4ea6-9a05-2577949d92cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_963b9916-428f-4202-83a7-6828402795e7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_963b9916-428f-4202-83a7-6828402795e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_2d2f1090-93eb-4e28-bea5-b01aa3c2dfc0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_2d2f1090-93eb-4e28-bea5-b01aa3c2dfc0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_dc3dc38f-b2b0-4162-a118-ac93fa59a349" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4dcaee8f-c3e1-4f89-8dbb-e4538df9cd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_dc3dc38f-b2b0-4162-a118-ac93fa59a349" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_e19f513f-4c82-44f0-8944-895fc0f8b377" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ea34d05d-0422-4ed9-8f70-aae47cc6e53f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_074a70cd-a124-4f59-ba49-f9d3030efdb7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ea34d05d-0422-4ed9-8f70-aae47cc6e53f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ea34d05d-0422-4ed9-8f70-aae47cc6e53f" xlink:to="loc_us-gaap_AwardTypeAxis_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af59aba7-5fa5-4af0-84ed-9b28a8653694" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f7ad0e8a-8443-4b00-8f94-3064c8ea41ad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af59aba7-5fa5-4af0-84ed-9b28a8653694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_ef3514bc-62d9-4a69-9bb8-f94b80e8407a" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsAndPerformanceStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af59aba7-5fa5-4af0-84ed-9b28a8653694" xlink:to="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_ef3514bc-62d9-4a69-9bb8-f94b80e8407a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockUnitsNarrativeDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockBasedCompensationRestrictedStockUnitsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockUnitsNarrativeDetails" xlink:type="extended" id="i023eba5b1af44c1c974dcff6932d8e6b_StockBasedCompensationRestrictedStockUnitsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_7299f662-5267-48fd-9e84-7d3b24a010c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_7299f662-5267-48fd-9e84-7d3b24a010c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_93ce26c9-5872-41df-8c74-b8d44cf83525" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_93ce26c9-5872-41df-8c74-b8d44cf83525" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_SharebasedCompensationArrangementsbySharebasedPaymentAwardPercentOfAwardTargetPerformanceMetric_ee73a40f-15dc-42b7-8450-8885c632ffa1" xlink:href="appf-20211231.xsd#appf_SharebasedCompensationArrangementsbySharebasedPaymentAwardPercentOfAwardTargetPerformanceMetric"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_appf_SharebasedCompensationArrangementsbySharebasedPaymentAwardPercentOfAwardTargetPerformanceMetric_ee73a40f-15dc-42b7-8450-8885c632ffa1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPercentOfCashBonusPaymentOnInitialTargets_3945551d-89d7-40f3-8bf5-6a2b46ed74b5" xlink:href="appf-20211231.xsd#appf_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPercentOfCashBonusPaymentOnInitialTargets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_appf_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPercentOfCashBonusPaymentOnInitialTargets_3945551d-89d7-40f3-8bf5-6a2b46ed74b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_d6542d70-275d-48ab-8f4b-1a4381dae39f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_d6542d70-275d-48ab-8f4b-1a4381dae39f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_0af5eccb-dcf2-45a1-a5eb-224f4d6548c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_0af5eccb-dcf2-45a1-a5eb-224f4d6548c7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_71eaa2e4-106c-4e45-b92a-2522c14391ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_71eaa2e4-106c-4e45-b92a-2522c14391ab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_7a08d484-6f6d-4f39-84e9-a3f5515cfa84" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_7a08d484-6f6d-4f39-84e9-a3f5515cfa84" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_c4e1d305-0fef-4679-8800-e5e9f6d0215f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_c4e1d305-0fef-4679-8800-e5e9f6d0215f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_307bd98e-1d49-407f-b284-e153c873a06e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_98ea1bfe-949e-461f-95dc-1f43e68d1510" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_307bd98e-1d49-407f-b284-e153c873a06e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_af3ef1b1-a317-45f2-99ce-cd576db9f0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_307bd98e-1d49-407f-b284-e153c873a06e" xlink:to="loc_us-gaap_AwardTypeAxis_af3ef1b1-a317-45f2-99ce-cd576db9f0cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af3ef1b1-a317-45f2-99ce-cd576db9f0cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_af3ef1b1-a317-45f2-99ce-cd576db9f0cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af3ef1b1-a317-45f2-99ce-cd576db9f0cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_af3ef1b1-a317-45f2-99ce-cd576db9f0cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_587d1a1a-c0f9-4e95-a848-b50e31c3881d" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsAndPerformanceStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:to="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_587d1a1a-c0f9-4e95-a848-b50e31c3881d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_51de28d7-b45c-4ba5-9b18-5b73a0b09f33" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_587d1a1a-c0f9-4e95-a848-b50e31c3881d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_51de28d7-b45c-4ba5-9b18-5b73a0b09f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_PerformanceStockUnitsMember_5b307ad1-025e-4c60-b4e4-7f94c0ef0a0e" xlink:href="appf-20211231.xsd#appf_PerformanceStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_appf_RestrictedStockUnitsAndPerformanceStockUnitsMember_587d1a1a-c0f9-4e95-a848-b50e31c3881d" xlink:to="loc_appf_PerformanceStockUnitsMember_5b307ad1-025e-4c60-b4e4-7f94c0ef0a0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_5d7aa309-2ea5-4b18-a243-d66501893c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:to="loc_us-gaap_RestrictedStockMember_5d7aa309-2ea5-4b18-a243-d66501893c3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsWithServiceConditionsMember_b8177aec-b70f-48cc-8b25-d35e90254738" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:to="loc_appf_RestrictedStockUnitsWithServiceConditionsMember_b8177aec-b70f-48cc-8b25-d35e90254738" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_RestrictedStockUnitsWithServiceAndPerformanceConditionsMember_d76324af-594c-44ee-b37e-3e971886a454" xlink:href="appf-20211231.xsd#appf_RestrictedStockUnitsWithServiceAndPerformanceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_758be897-b9f1-45f9-83c9-304d5077373d" xlink:to="loc_appf_RestrictedStockUnitsWithServiceAndPerformanceConditionsMember_d76324af-594c-44ee-b37e-3e971886a454" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_08ecda47-732a-44b6-8c34-da01aabd4855" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_307bd98e-1d49-407f-b284-e153c873a06e" xlink:to="loc_srt_RangeAxis_08ecda47-732a-44b6-8c34-da01aabd4855" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_08ecda47-732a-44b6-8c34-da01aabd4855_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_08ecda47-732a-44b6-8c34-da01aabd4855" xlink:to="loc_srt_RangeMember_08ecda47-732a-44b6-8c34-da01aabd4855_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_451581da-8605-4171-bedf-433155db15fd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_08ecda47-732a-44b6-8c34-da01aabd4855" xlink:to="loc_srt_RangeMember_451581da-8605-4171-bedf-433155db15fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_7785eeef-4c5a-44f5-9f5c-132f51633bff" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_451581da-8605-4171-bedf-433155db15fd" xlink:to="loc_srt_MinimumMember_7785eeef-4c5a-44f5-9f5c-132f51633bff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_afb3fcaa-a383-41be-aa39-e6761ad77f33" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_451581da-8605-4171-bedf-433155db15fd" xlink:to="loc_srt_MaximumMember_afb3fcaa-a383-41be-aa39-e6761ad77f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_40df7eea-c20c-45cb-bc99-a0fed9c01be1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_307bd98e-1d49-407f-b284-e153c873a06e" xlink:to="loc_us-gaap_VestingAxis_40df7eea-c20c-45cb-bc99-a0fed9c01be1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_40df7eea-c20c-45cb-bc99-a0fed9c01be1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_40df7eea-c20c-45cb-bc99-a0fed9c01be1" xlink:to="loc_us-gaap_VestingDomain_40df7eea-c20c-45cb-bc99-a0fed9c01be1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_77a5fc84-1149-474f-ad7b-fdac8af01637" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_40df7eea-c20c-45cb-bc99-a0fed9c01be1" xlink:to="loc_us-gaap_VestingDomain_77a5fc84-1149-474f-ad7b-fdac8af01637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8e8d2e0e-165d-46f9-bf47-850ecdfdd190" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_77a5fc84-1149-474f-ad7b-fdac8af01637" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8e8d2e0e-165d-46f9-bf47-850ecdfdd190" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_85039945-8656-46c2-8e6e-451f608ff6ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_77a5fc84-1149-474f-ad7b-fdac8af01637" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_85039945-8656-46c2-8e6e-451f608ff6ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_1a1745cc-a113-4cda-a31e-d352d0faddc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_77a5fc84-1149-474f-ad7b-fdac8af01637" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_1a1745cc-a113-4cda-a31e-d352d0faddc7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockAwardsDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#StockBasedCompensationRestrictedStockAwardsDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/StockBasedCompensationRestrictedStockAwardsDetails" xlink:type="extended" id="icf293ef7590c4a14ba2e86db3e758f25_StockBasedCompensationRestrictedStockAwardsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_809f317c-affb-47f4-822c-864693642992" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_809f317c-affb-47f4-822c-864693642992" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3fe1dcad-297d-48c3-b761-391cc9586705" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3fe1dcad-297d-48c3-b761-391cc9586705" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_73281070-91e2-477a-9014-a447fa7557f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_73281070-91e2-477a-9014-a447fa7557f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_74a9b9dc-36c2-4356-b2c6-e9f18cd0575b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_74a9b9dc-36c2-4356-b2c6-e9f18cd0575b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_cde728e6-e7d0-4388-9e7a-632ab2c9af80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a5d76531-7f7c-4a37-bd12-69337bcce095" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_cde728e6-e7d0-4388-9e7a-632ab2c9af80" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c1df0d64-346e-463f-aafb-45e6dd96777e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_809f317c-affb-47f4-822c-864693642992" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_14835c23-dbd3-4524-8369-7ad4f01ac713" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_14835c23-dbd3-4524-8369-7ad4f01ac713" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_97d65445-a245-4705-8533-02f8a9921362" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_97d65445-a245-4705-8533-02f8a9921362" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_1003cd75-a6b0-4ebe-90ee-9f9b4bf220f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_1003cd75-a6b0-4ebe-90ee-9f9b4bf220f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_cee78720-ff8f-4436-a19c-7b0945f125a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_91213d73-45e6-4ed7-98bc-c2acc93de695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_cee78720-ff8f-4436-a19c-7b0945f125a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_7346c6f9-01e6-4998-a9b1-902c8401765f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f1b266f9-4b36-4a0b-a9cb-08935e7be68a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_809f317c-affb-47f4-822c-864693642992" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f1b266f9-4b36-4a0b-a9cb-08935e7be68a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_94fafd21-edc8-45f5-afa6-10a1decc2107" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f1b266f9-4b36-4a0b-a9cb-08935e7be68a" xlink:to="loc_us-gaap_AwardTypeAxis_94fafd21-edc8-45f5-afa6-10a1decc2107" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_94fafd21-edc8-45f5-afa6-10a1decc2107_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_94fafd21-edc8-45f5-afa6-10a1decc2107" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_94fafd21-edc8-45f5-afa6-10a1decc2107_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dc1c5caa-8bad-4612-8537-8c8f8af3b08b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_94fafd21-edc8-45f5-afa6-10a1decc2107" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dc1c5caa-8bad-4612-8537-8c8f8af3b08b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_2193b1bc-6efc-42dc-a7cd-45e96efa49fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dc1c5caa-8bad-4612-8537-8c8f8af3b08b" xlink:to="loc_us-gaap_RestrictedStockMember_2193b1bc-6efc-42dc-a7cd-45e96efa49fc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended" id="ia78702847a7a4b6897f9020d55f0a210_IncomeTaxesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_0f45b504-ccd4-47e1-b66c-811018a0a56d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_0f45b504-ccd4-47e1-b66c-811018a0a56d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_59cf3c97-2e02-4954-9e32-a9f384df87be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_OperatingLossCarryforwards_59cf3c97-2e02-4954-9e32-a9f384df87be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_0dd00724-3c33-46f7-ad9f-b5fe9d6b0d61" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_0dd00724-3c33-46f7-ad9f-b5fe9d6b0d61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilities_2e53970f-6531-4396-8e17-08ce5fbe0e38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_DeferredTaxLiabilities_2e53970f-6531-4396-8e17-08ce5fbe0e38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued_235d7544-a57f-4094-89e4-d7d10d273701" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued_235d7544-a57f-4094-89e4-d7d10d273701" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_6cab74d3-13bf-4303-9c03-62563cb7dbe2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_fdca276d-9bcb-4fd6-9ce3-751ba44c4c9d" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_6cab74d3-13bf-4303-9c03-62563cb7dbe2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_0c7336cd-d506-4acb-b4cb-40b55d9940ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_6cab74d3-13bf-4303-9c03-62563cb7dbe2" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_0c7336cd-d506-4acb-b4cb-40b55d9940ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_0c7336cd-d506-4acb-b4cb-40b55d9940ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_0c7336cd-d506-4acb-b4cb-40b55d9940ee" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_0c7336cd-d506-4acb-b4cb-40b55d9940ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_ad9676b8-28ba-4323-b5d3-2eb0e24950a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_0c7336cd-d506-4acb-b4cb-40b55d9940ee" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_ad9676b8-28ba-4323-b5d3-2eb0e24950a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_2d04ea14-bb3f-4920-9855-7a2e9c2350c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_ad9676b8-28ba-4323-b5d3-2eb0e24950a3" xlink:to="loc_us-gaap_DomesticCountryMember_2d04ea14-bb3f-4920-9855-7a2e9c2350c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_32700370-90b9-4ef0-a5c9-6c303db6c488" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_ad9676b8-28ba-4323-b5d3-2eb0e24950a3" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_32700370-90b9-4ef0-a5c9-6c303db6c488" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_77ca741b-fa62-4ae7-9428-07f15a7d7175" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_6cab74d3-13bf-4303-9c03-62563cb7dbe2" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_77ca741b-fa62-4ae7-9428-07f15a7d7175" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_77ca741b-fa62-4ae7-9428-07f15a7d7175_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_77ca741b-fa62-4ae7-9428-07f15a7d7175" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_77ca741b-fa62-4ae7-9428-07f15a7d7175_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_a13c9093-94c5-4850-b26e-40a7f44f079c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_77ca741b-fa62-4ae7-9428-07f15a7d7175" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_a13c9093-94c5-4850-b26e-40a7f44f079c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchMember_76617e95-ad56-404f-8e81-184c179b7f57" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_a13c9093-94c5-4850-b26e-40a7f44f079c" xlink:to="loc_us-gaap_ResearchMember_76617e95-ad56-404f-8e81-184c179b7f57" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.appfolio.com/role/RevenueandOtherInformationDetails" xlink:type="simple" xlink:href="appf-20211231.xsd#RevenueandOtherInformationDetails"/>
  <link:definitionLink xlink:role="http://www.appfolio.com/role/RevenueandOtherInformationDetails" xlink:type="extended" id="i007b5eac67d24d069c9f02c9cfffb841_RevenueandOtherInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductInformationLineItems_38997a2e-68c0-4ed8-a966-c90bfc1b292b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProductInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e0b3907f-da94-4734-bb49-5a61d9d1d988" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_38997a2e-68c0-4ed8-a966-c90bfc1b292b" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e0b3907f-da94-4734-bb49-5a61d9d1d988" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfProductInformationTable_3562a985-8290-4327-a369-3e16a4b0a5de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfProductInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductInformationLineItems_38997a2e-68c0-4ed8-a966-c90bfc1b292b" xlink:to="loc_us-gaap_ScheduleOfProductInformationTable_3562a985-8290-4327-a369-3e16a4b0a5de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_3562a985-8290-4327-a369-3e16a4b0a5de" xlink:to="loc_srt_ProductOrServiceAxis_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743" xlink:to="loc_srt_ProductsAndServicesDomain_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_02cfd73b-17a2-4cf1-95f3-f2b9103da72b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_ea4b3b48-1bea-4aff-b69d-c1cf9a44b743" xlink:to="loc_srt_ProductsAndServicesDomain_02cfd73b-17a2-4cf1-95f3-f2b9103da72b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_CoreSolutionsMember_8d433e2f-8b4a-4ef7-8ff0-02e0686372d4" xlink:href="appf-20211231.xsd#appf_CoreSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_02cfd73b-17a2-4cf1-95f3-f2b9103da72b" xlink:to="loc_appf_CoreSolutionsMember_8d433e2f-8b4a-4ef7-8ff0-02e0686372d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_ValuePlusServicesMember_9df89d7e-130b-4f42-9ba1-00eb1931bd6f" xlink:href="appf-20211231.xsd#appf_ValuePlusServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_02cfd73b-17a2-4cf1-95f3-f2b9103da72b" xlink:to="loc_appf_ValuePlusServicesMember_9df89d7e-130b-4f42-9ba1-00eb1931bd6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_appf_OtherServicesMember_c99fe4a7-5228-4a2b-9158-40ed6ca97de2" xlink:href="appf-20211231.xsd#appf_OtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_02cfd73b-17a2-4cf1-95f3-f2b9103da72b" xlink:to="loc_appf_OtherServicesMember_c99fe4a7-5228-4a2b-9158-40ed6ca97de2" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
