Something equally accesible by any legitimate participant.

Freely available, usually used in a sexual sense. Comes from English Grouse hunters expression to identify a bird that is a legitimate target as opposed to a bird that is injured, too young etc.

An opportunity, that might be presented by another's carelessness.
An opportunity which can be taken without repurcussions.

available, desirable, ok to approach, or to speak of

Girls who are up for grabs.

OK to shoot. Comes from animal hunting - yuk.

The Fair's Fair Game (titled as such because of the 'equivalent exchange' rule) is a game that was popularized by the uprising of picture messaging, though the exact origins or time period of the game are unknown. The game's rules are applicable to near any social situation, but is most commonly used in the transfer of revealing photographs (I.E-Pornography). In this version, Person A and Person B both swear an unspoken oath to uphold the game's rules. After such, Person A sends a picture of near anything (whether it be a body part, a plant, or other plausible object/scene), in which Person B will recieve it, and reply with a similar picture. In this fashion, boundaries are gently removed so that both party members feel secure about their decisions, and do not feel swindled or coerced into a bad situation. The Fair's Fair game may also be used with simple text (I.E - secrets). As stated before, it's a simple gesture of exchanging one tidbit of information for another, but at a gradual progression.