Werewolf is a form of LARP in which a group of players model a village being terrorized by a Werewolf. One player is secretly designated the Werewolf and the other players must attempt to determine who it is. The game is more commonly called Mafia outside of the confines of a Scifi convention.

It is most commonly recognized by outsiders when it is noticed that a circle of people somewhere at the con all has their heads down, with another individual whispering at them. For details on how to play, the Wikipedia article should have sufficient detail to get you started.