A role-playing game (RPG) is a game in which each participant assumes the role of a character, generally in a fantasy or science fiction setting, that can interact within the game's imaginary world.
Games like Dungeons and Dragons, Battletech and Star Wars were all popular examples of the genre of early online role playing games.
MUDs and MOOS evolved into Massive Multiplayer Online Role-Playing Games (MMPORGs), where users play a version of a game that includes access to a persistent world online through the game's interface.
Ultima Online and Neverwinter Nights were popular early in the development of MMPORGs. Everquest's much improved graphic engine drew even more players. World of Warcraft, an extremely popular MMPORG created by Blizzard software, now boasts over 6 million subscribers. Millions of players are involved in other games as well, especially in South Korea, where these games have proved especially popular, due in part to the high rate of broadband adoption in that country.
RPG also stands for Report Program Generator.