(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.

(video games) A video game designed to convey an aesthetic and provoke a reaction, rather than to provide a traditional diversion with set goals.

A motion-sensitive camera placed on animal trails to photograph passing wildlife.

A game of skill which requires the bettor to guess which of three small cups (or shells) a pea-sized object is concealed under, after the party operating the game rapidly rearranges them, providing opportunity for sleight-of-hand trickery.

(video games) A computer or video game of the genre characterized by investigation, exploration, puzzle-solving, interaction with game characters, and a focus on narrative rather than reflex-based challenges.

Alternative form of head-game

(idiomatic) A foolish, profitless, or hopeless undertaking.

simple past tense and past participle of game the system

(informal) An attempt to psychologically manipulate or intimidate someone. / A mental pursuit or obsession. / Skill at fellatio.

To use the rules and procedures meant to protect a system in order to instead manipulate the system for a desired outcome.