The Full form of APK is Android Application Package. An APK file is the package file format used by the Android operating system for installation and distribution of mobile games, mobile apps, and middleware. APK file format is analogous to other software packages such as a Debian package in Debian-based operating systems or APPX in Microsoft Windows. A program for Android is first compiled using Android Studio to make an APK file, and then all of its parts are packaged into one container file.
An APK file contains all of a program’s code such as .dex files, certificates, resources, assets, and manifest file. As applicable in the case with many file formats, an APK file may have any name needed, but it is required that the file name ends with “.apk” in the file extension for being recognized as such. An APK file can also be saved in compressed zip format, with any unzip tool or decompression it can be opened.
The user can open the file either directly using unzip tools or by changing the extension to .zip. They are a type of archive file. When the user is downloading and installing an android application then actually he is installing an APK file. The user can install an APK file from a file manager app without downloading or directly from a desktop.