Live-action roleplaying games, called "LARPs" for short, are a singular phenomena. They take the situations and some of the mechanics from
tabletop roleplaying games (that is, those played with
paper,
pencil and
dice) and allow the players to act out much of the action of the game. The result resembles
improvisational acting quite strongly: players create characters for a particular game, and then start to move, speak and act as those characters would.
It should be noted that if the development of the game leads to a situation where violence would be employed, the players do not whip out guns and start shooting one another, or start beating each other up, or anything of the sort. Each game has a different system for resolving combat, simulating supernatural abilities, and the like; White Wolf Game Studio's live action system has players use rock-paper-scissors to resolve these situations, with a complex system of bidding traits to account for differences in ability level between characters.
People who play live-action roleplaying games often find that they have a chance to get into character more deeply than in tabletop games, and find that this emphasis on characterization helps prevent the descent into hack-and-slash gaming as is often found in poor-quality Dungeons & Dragons sessions.
The most commonly-played LARP is a live-action version of White Wolf's Vampire:The Masquerade, but there are many other games as well, such as Werewolf, Changeling, Wraith, and (coming in 2001) Mage. There are a number of non-White Wolf live-action systems available as well, such as In Nomine and Purgatory.