Definition:
Our dictionary says that a trap is 'a device for catching animals'. Substitute the phrase 'unwary chess players' for the word 'animals' and we have a good definition of a chess trap. A chess trap has a large element of surprise; the trapped player didn't notice anything special, but the position is suddenly, completely, irrevocably lost.
Chess traps are a special branch of opening theory, even though they can be set at any time in the game. When they occur in the middle or end game, we usually call them swindles. A trap is almost always the result of a bad move, or blunder, and when a game ends abruptly in the opening, it's known as a miniature.
