Definition of metagame:
(n) :
(countable, uncountable) The 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.
(v) :
(roleplaying games) Of 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.
(n) :
(countable) A game about games.