Definition from Wiktionary, the free dictionary
- (poker) An impassive facial expression cultivated to prevent other players from determining whether one's actions in the game are the result of a quality hand, or of bluffing.
- Though he thought he had a perfect poker face, he had a number of tells his opponents soon learned.
- Any similar expression used to prevent giving away one's motives, feelings, or situation.
Derived terms 
Impassive facial expression preventing determining whether one's actions in the game are the result of a quality hand or of bluffing