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1.
MGO
Metal Gear Online, the Online feature for Metal Gear Solid 3: Subsistence.
Wanna play Deathmatch, Team Deathmatch, Rescure, Sneaking, or Capture in MGO?
by Durango June 02, 2006
 
2.
MGO
Short for "Metal Gear Online". MGO was offered for one year after the release of "Metal Gear Solid 3: Substance".

Now, MGO is back in the game "Metal Gear Solid 4: Guns of the Patriots".
Have you played MGO lately?

Yes I have, I came in number one during a Death Match.
by Robert Brunello June 15, 2008
 
3.
mgo
abbreviation for massive gay orgy!
hey john, we're goin over joe's house for an mgo with farm animals!
by CHINS May 21, 2005