Wad(n.)1: A data file for id Software's incredibly popular 'Doom' series of games first released in 1993. The term ".Wad" is short for "Where's all the data?" They can be used to distribute user created content as well and thus spawned the videogame modding phenomenon. As of 2006 there are thousands of user created .wads avalible for download.
Person1: "Hey, did you check out that new .wad for doom 2?"
Person2: "Yeah it was a pretty sweet deathmatch map!"
Person1: "Doom forever!"