Definitions
1.NounA game about games."Nomic is a metagame in which players can modify the rules as part of gameplay."
2.NounThe exploitation of the rules etc. of some other game, at a higher level than simply playing the game normally; a game outside or peripheral to the actual gameplay.
3.NounThe conventions of a gaming community; the characters, weapons, techniques, etc, which are currently considered most viable in multiplayer gameplay, and the best practices for using them.
4.VerbOf a roleplayer, to make use of knowledge while roleplaying that they learned out of character, which their character does not know; often considered a form of cheating.