An acronym for "Massive Multiplayer Online Role Playing Game". Players play the video game competing against and cooperating with other players connected to an online network. Most require players to purchase the software and pay a subscription fee to participate.
Some eaxamples are
EverQuest, World of Warcraft,
Ultima Online,
Star Wars Galaxies among others. These games have spawned a sub-culture of gamers with many of their own words and phrases unique to the experience.