Android application package (APK) is the package file format. It is used by the Google's Android Operating System for distribution and installation of Mobile Apps. It is also used for middleware. APK files are an archive file, in zip format packages based on the JAR file format.It is having .apk as the filename extension.
To make an APK file, a program for Android is first written. Then all of its parts are combined into one file. An APK file contains all program codes, resources, assets, certificates, and manifest file. APK files can have any name needed, provided that the file name ends in ".apk". APK files can be installed on Android-powered devices as we install software on our PC.