mod - modification

Definition: Gamers have a long history of finding ways to alter, tweak, or otherwise modify game software to suit their purposes. User-created additions and modifications to a video game have become known simply as "mods." Many games are now designed to make it easy for ambitious members of the community to access various aspects of the game code and other game resources. It is possible to alter some games to the extent that they are scarcely recognizable. This can include adjustments to the engine, customized graphics and sounds, user-made maps, and unique storylines. Sometimes the mod grows to be more popular than the original game, as is the case with Counter-Strike, which began as a modification for Half-Life.