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