What is an APK file?

An APK file is the installation file for an Android app. It contains everything Android needs to install and run an app on your device. Put simply, it is the Android equivalent of a classic installer file on a computer. Even if you usually install apps through Google Play, the end result on the device is technically an APK-based installation package. An AAB file, by contrast, is a publishing format for developers and cannot be installed directly on the device.