role-playing game, R.P.G., RPG, n. a genre of game in which players assume the personae of characters in a story, the outcome of events in said story being determined by a player called the referee or gamemaster; RPGs are often played according to complex and voluminous sets of published rules, charts, and other sundry materials; examples include Advanced Dungeons & Dragons, Champions, GURPS, and the World of Darkness games. See also LARP, tabletop RPG. [GJ1]

Addendum: There are two other definitions which sometimes crop up. Militarists know RPG as the abbreviation for “Rocket Propelled Grenade” (ie a bazooka), and the other is a class of video game which most self-respecting table-top RPG buff does not consider a true RPG.