Definition of trap
A "trap" in English is like a trap in French. What is meant by a trap is a play that hints at a weak hand. If a player plays passively, as if he were weak, hoping to be bluffed, he is said to be playing the trap. There are several reasons to play the trapdoor. One of them is when we are playing against a very aggressive player and we are out of position. Usually, very aggressive players will tend to bluff in position. To protect his range, a player can play passively when he has a weak hand and when he has a very strong hand (trap).
An example of a trap
A player calls the raise from the very aggressive button in SB position. The player in SB position has 99. The flop drops 9-8-3. The action on the flop is check, bet, call. The turn is an A and the player in SB position checks again. The button bets and the player in SB position calls. The river is an 8 and the player in SB position checks again. This is what we call a trap game. Obviously, the SB player has a very strong hand. Normally he would have bet. But he suspects that the player on the button is trying to bluff him on the river, so he checks to make him do so.