JupiterMGO usually refers to young adult males that pose as female gamers in any online type of game. This is only usually done to get people to look at certain things like youtube pages and things of that sort.
After being revealed as a male, this male usually only plays the game with people who are very good at it, and will most likely never play with his long time friends ever again.
"Dude I just found out about this girl on Metal Gear Online. Her name is Erika and she's so hot, check out her youtube page it's.
(Two weeks later) Dude I just found out 'Erika' is a guy! What a JupiterMGO!...Oh well at least the pictures from his youtube page is of a hot girl."