A mod is a change in one or more aspects of a video game, such as the way the game looks or interacts, made by a player or fan of the video game. Modifications can range from minor changes to complete overhauls and can add value and fun to the game.
Android applications are packaged into an Android Package file that contains the entire contents of the application. So we call them apk mod files, and it can be installed on Android mobile devices.
If the APK is the installation file of an application, the Mod APK is simply the installation file of that application, but has been changed (Modification). It can be a modified version of any official Android app, from social networks like Instagram, WhatsApp, PicsArt, etc. to games like Angry Birds, Bejeweled, etc.