MMORPG's (Massively Multiplayer Online Role Playing Games) are RPG's that are played online in servers with hundreds of other players, as opposed to just playing them by yourself (or with a few friends in LAN).
(posted by Anyonmouse) I know I spelled it wrong ]
An example:
Diablo = rpg
WoW = MMO.
Another good mmorpg is warhammer online, i don't know what apb classes as, its either mmotps or something (could be mmo too)
It's been a while since Blizzard released a new Diablo (the last one was released in 2000), but it was a great game back then, since it was one of the first to include good LAN support.
Blizzard are also set to release Diablo 3 sometime soon, which looks pretty good.
Rohan Online >.< It was grand but they just won't fix the class imbalances and YNK turned it to pay to win ._. hate templars. This is the longest one I played I think?
Then there's Ragnarok and a few others.. Forsaken World is just a prettier version of Perfect World.. blah.