Is short for modifications, and is when a current game is modified by changing the items, characters, enemies, models, textures or storylines. Mods can extend the life of a game and are often published over the Internet.
Reworks of a program that usually target a specific theme or idea. Mod communities spring up around a game because people like to modify the original game to make it more interesting to a specific group.
The definition of this terms used to quite clear; when somebody MOD ified and existing game. The exact type of modification could include new textures, enemies, weapons or even gameplay features. For example when Doom 3 was released there were quite a few Flashlight Mods released. These allowed players to attach a working flashlight to any weapon instead of the default option which meant having to switch from weapon to flashlight (Very, very annoying and totally unrealistic). However, the release of half-Life 2 has confused matters slightly. In this case a Mod is a self-contained mini-game that may or may not make any changes to the game. For example it could just be a collection of maps. The difference between a map and a mod in this case is that the mod appears on the games list within Steam. It makes life much easier for the end user. In my opinion it's a pity they didn't create a new name for this to avoid confusion with other game s and engines.