APK - Android application package
Android application package is a file extension of the application (app) or middleware file that could be directly installed on the Google's Android operating system. '.apk' file in android OS is analogous to .exe file in Windows, as both of them represents the executable or installable files. ".apk" files are zipped archive files which are based on the JAR file format.
Usually to install any application on an android device, we go to the "playstore". But, alternately if we want to install some app offline or directly from the app publisher, we require an .apk file of that app. If you have an APK file, you may go on with an installation directly, without connecting your device to the internet.
How to install an .apk file on android system
To install an apk file, first you need to open an APK installer app. Then, you need to navigate to a place where you have your .apk application file. Now just click on the application file and select the install button. Your app will be installed in few seconds or minutes.