Massively Multiplayer Online Role Playing Game - aka where nerds become virgins. I should know, I used to be one. Usually these games are, well, massive online games which see large amounts of players cooperate and battle against each other for loot, story, or fame.

Typically paid for via a subscription model, these games typically have large time requirements and some ability to be sociable online. They are almost never designed for solo play. The games are usually designed to extract your time, wealth, happiness, and joy from your ever-living soul. But the bonds of friendship you make can last a lifetime.

Famous examples include:
World of Warcraft
EVE Online
Destiny