Massive Multi-player Online Role-Playing Game - Massively multiplayer online role-playing game (MMORPG) is a genre of role-playing video games in which a very large number of players interact with one another within a virtual game world.
As in all RPGs, players assume the role of a character (often in a fantasy world) and take control over many of that character's actions. MMORPGs are distinguished from single-player or small multi-player RPGs by the number of players, and by the game's persistent world (usually hosted by the game's publisher), which continues to exist and evolve while the player is offline and away from the game.
MMORPGs are played throughout the world. Worldwide revenues for MMORPGs exceeded half a billion dollars in 2005, and Western revenues exceeded US$1 billion in 2006. In 2008, Western consumer spending on subscription MMOGs grew to $1.4 billion. World of Warcraft, a popular MMORPG, has more than 10 million subscribers as of February 2012. Star Wars: The Old Republic, released in 2011, became the world's 'Fastest-Growing MMO Ever' after gaining 1 million subscribers within the first three days of its launch.
Source:http://en.wikipedia.org/wiki/Massively_multiplayer_online_role-playing_game