Gamers Glossary: Semi Co-Operative Games

Semi Cooperative Game:
A usually brutal variant on co-operative games in which, while most players are acting co-operatively, one or more players are secretly working against the others, as "traitors" or other nefarious folks. These nasty folk win the game by making the others lose. Assigned randomly at the start of the game (usually by a card drawing mechanic), they are hidden - gaining bonuses if they stay anonymous despite their misdeeds, whereas the "loyal" players will gain a bonus if they uncover the traitor.
(examples of these games are Shadows Over Camelot and Battlestar Galactica)