Modding in Grand Theft Auto

Grand Theft Auto is a series of video games created by a company named Rockstar Games. The game is very popular in the world. Due to this popularity it has become a platform to develop small programs which are called mods. The full form is modifications. The name itself suggests that it makes small modifications in the game and gives it special abilities which have not given by the creators. 
There are several websites on the web which provide mods of most of the GTA games. Some mods are installed externally in the game directory while installing some mods require to replace it with an original file.
People could install many mods and create their own GTA with new players, missions, etc. The web is already filled with many mods.