In the simplest of terms, a poker trap is a manner of play that misrepresents one’s hand, showing it to be much weaker than it actually is, with the aim of getting the opponent to commit more chips to the pot.
To accomplish this goal, poker players will resort to different strategies, such as checking with a monster or just calling an opponent’s bet instead of raising disguising the real strength of their hand.
For example, a player on the button raises with pocket 4s, and the player in the big blind 3-bets with pocket aces. The button player calls, and the flop comes K 4 2, rainbow.
The big blind player fires a big continuation bet. Instead of raising and alarming the player in the big, the button player just calls and sets the trap. This allows the player in the BB to keep betting both for value and as a bluff on future streets, even with the hands that would have folded to a raise, giving additional value to the player who is trapping.
With the way the action developed up to this point, there is no reason for the player with pocket aces to think they don’t have the best hand. The button player kept his flopped set disguised, and they’ll spring the trap on the turn or the river, allowing their opponent to commit more chips to the pot before doing so.