Gamer jargon. Someone who uses the most cheap and overpowered weapons/set up, items to win a game. It could be used in a general sense as well with someone who uses a cheap tactic or items to overpower the competition rather than using skill.
Example: In Mass Effect 3 Multiplayer
player 1: I'm going Harrier TGI
player 2: Going full cheese I see...
It is the combination of just the right amount of garlic, cheese and bread all in one. It is truly a delicacy for the ages and shall be enjoyed by people far and wide.