bluff : In the card game of poker, to bluff is to bet or raise with an inferior hand. This is useful because it can cause other players to believe the bluffing player has a dominant hand, so that they all fold; the bluffing player then wins the pot. By extension, the terms are often used outside the context of poker to describe the acts of pretending knowledge one does not have, or making threats one cannot execute.
Pure bluff : A pure bluff, or stone-cold bluff, is a bet or raise with an inferior hand that has little or no chance of improving. A player making a pure bluff believes he can win the pot only if all opponents fold. The pot odds for a bluff are the ratio of the size of the bluff to the pot. A pure bluff has a positive expectation (will be profitable in the long run) when the probability of being called by an opponent is lower than the pot odds for the bluff.