'Mafia' can be used to refer to the genre of games which function as a competition between an informed minority and an uninformed majority, most basically that's the common theme between all mafia genre games. The earliest Mafia games were just a handful of players assigned as Mafia vs. the Citizens, but the game evolved to include roles like Sheriff, Mayor, Godfather, etc . . . Further spinoff version following the same basic format have been born as well, such as Werewolves vs. Peasants for example.
I found a wiki on Mafia once, but I'm not sure where it is.