RPG / Roleplaying
From Wikipedia, the free encyclopedia:
A role-playing game (RPG; often roleplaying game) is a game in which the participants assume the roles of fictional characters and collaboratively create or follow stories. Participants determine the actions of their characters based on their characterization, and the actions succeed or fail according to a formal system of rules and guidelines. Within the rules, players can improvise freely; their choices shape the direction and outcome of the games.
Say, the players decide to be musketeers in 16th-century France. One of them is designated a game master; his job is to devise a suitable challenge (perhaps a plot against the king), and all the necessary details, such as significant locations, events, secondary characters, etc. The other players create a protagonist each, and play their parts to bring the adventure to life. The GM describes the situations that arise and decides the outcomes of their actions. The rules can be very simple ("use you common sense!") or very complex, based on math formulae and rolling dice.
(For the modern, busy player who may have a hard time finding and keeping a local gaming group, virtual tabletops look like an attractive option. But it's an option I haven't tried yet.)