A key concept in the later work of [Ludwig] Wittgenstein. According to his famous analogy between using language and playing games, we have in both various sets of rules or conventions, and these determine what moves are permissible or impermissible, successes or failures, each set of rules identifying a distinct game.
A given move can be judged only according to the rules of the game to which it belongs. Many time-honored philosophical problems result from judging moves in one game by the rules of another, and can be dissolved only by systematic clarification of the relevant differences; hence such clarification should be philosophy’s main concern.
From A Dictionary of Philosophy (Rev. 2nd ed.) ed. Antony Flew (St. Martin’s, 1979), 196.