Well, not everyone know what is a Mod APK and that is why exactly I am here to educate you on this.
A Mod APK such as a GCam APK is a modified app or game on Android that is done by some developer who knows how to do that.
Usually these modified apks bring paid apps for free, unlimited in-game money and resources etc.
If you are new here and want to try this out, then Download Mod APK of any app or a game and see it by yourself.