Definition of bluff
A bluff in poker is when you represent a hand that you don't have. The goal is to make your opponent believe that your hand is stronger than it really is by betting. To call a bluff, there must be a bet and the intention to deceive. Bluffing can be seen as lying.
An example of a bluff
Bluffing is an important aspect of poker. A player who never bluffs would lose out on great opportunities to make money. Like any aspect of poker, however, it is important to call your bluffs, that is, to bluff with credible frequency. A player who bluffs on every hand will eventually become unsuccessful with his bluffs. For a bluff to work, it must be believable. A classic example of a bluff is when we miss a draw on the river. We are in position and bet the flop with a flush draw. Our opponent calls the bet. The turn is a brick and the action is the same. On the river, another brick. We missed our draw and our hand is too weak to win on the showdown. Betting all in to represent a lot of strength is called a bluff. Whether it works or not, the bluff is still a bluff.