Noun
(uncountable) A chess opening characterized by the moves 1.e4 e5, in which both White and Black move their king's pawn to the fourth rank with their first move.
(countable) Any of the set openings which begin in this way. (Ruy Lopez, Scotch Game, etc.)
open game (plural open games)
Alternative letter-case form of Open Game
These rules formed the basis of the d20 System which is available under the Open Game License (OGL) for use by other publishers. Source: Internet
Cook; "The Open Game License as I see it". Source: Internet
Without having any particular dogma or position other than to “keep first-person shooters interesting,” the open game jam carries a subtext of letting preconceptions about FPSs go, simply by cultivating a temporary creative zone for new ideas. Source: Internet
That makes them open game. Source: Internet