AAR (Android Library Archive) is a package file format, similar to APK (Android package) file format, that you can use as a dependency for an Android app module
AAR (Android Library Archive) is the binary distribution of an Android library project. AAR file is variant of jar file similar to apk. AAR files can contain Android resources and a manifest file, which allows you to bundle in shared resources like layouts and drawables in addition to Java classes and methods.
AAR file is used to share resources between multiple Android applications or between multiple versions (for example free and paid) of same Android application.