A "Massively Multipler Online Roleplaying Game" is a popular genre of online gaming. Normally, you create one or more characters and play along according to the storyline, and do different activities depending on what the game's theme is.
E.g. Nexus, a 2d mmorpg, is a game where you explore the magical world of ancient Korea, and is highly community based. Try things like woodcutting, monster hunting, joining clans and armies, and others, all with a very personalized character. Earn money, trade with other players and play various games like Bloodlust and Elixir wars in the the three Kingdoms of Buya, Koguryo and Nagnang!