APK stands for Android Package Kit, a software extension. It is also known as Android Application Package; in simple words, it is the format of files. Its function is similar to the software in computers. APK file is designed for Android Operating System. You can also use the file with other operating systems, but android is the best operating system for apk files.
The purpose of the APK file is to install and distribute several mobile apps. It helps you install third-party apps not available in the Google Play Store. These third-party apps can only be executed on Android Operative System with the help of an APK file with an extension of .apk. This extension contains all the necessary resources to run any app on your android device. Some of the resources the apk extension holds include application code, assets, AndroidManifest.xml, and resources—arc, manifest file, etc.
Apk files may come with any name, but the extension is necessarily .apk. Several websites allow users to download apk files directly. Be careful while using these apps, as they may contain malware that may harm your device.