APK (Android Package Kit) file extension is used by Android package files for Google Android mobile application distribution and installation purposes. APK package files can be seen as counterparts to EXE installation files used by Windows operating system. Single APK package store relevant code along with necessary resources in the form of files (AndroidManifest.xml, classes.dex, resources.arsc) and folders (META-INF, lib, res).

APK package files are created using Android Studio, the official Integrated Development Environment (IDE) for Android app development. Finished application can be stored in APK package and then published on Google Play service after being digitally signed for release.

APK file format limitations

APK files to be published on Google Play cannot be larger than 100 MB, a limition that can be a problem for software engineers. However, Google Play allows additional files for larger resources (multimedia, hi-res graphics, etc.) required by an application to be added without violating the size limit.

ZIP compression and relationship with JAR format

APK format is based on JAR format and uses ZIP compression. Any APK package can be opened using various ZIP tools.

APK files aren’t commonly encountered by the users as typically Android app are downloaded and installed by Google Play in the background. Some websites, however, offer option to manually download and install APK packages.