1, mod is a game term, which means game module. It is a modification or enhancement program of the game, by modifying props, weapons, characters, enemies, things, patterns, story lines and so on. In computer games, or add new props and things.
2. Most game modules are made by third parties, which can not only improve the playability of the game, but also some MODs can even turn the original game into a new set of works.
3. All modules are additional supplements, not modifications to the original version.