Slow play
Underplaying a monster to disguise it and trap. Cute, but it often just lets opponents draw cheap.
Raise from the cutoff with A♣A♠ and the button calls. The flop comes A♦8♣3♥ — dry, rainbow, no draw for anyone. You've flopped top set, about as far ahead as you get on that board. So you check. The button checks back with air, or bets a pair of eights that would have folded to a bet — and the hand you'd have won small stays in the pot instead.
That's the only spot the move works: you're so far ahead nothing behind can catch up in one card, and the opponent bets when you'd rather they didn't fold. Checking turns one street of value into two, or lets a bluff live in a pot you'd have shut down by betting. You give up a certain small bet now for a shot at a bigger one later. Sometimes that trade is worth making.
Beginners run it on the wrong board. Slow-play kings on Q♥J♥4♣ and you hand a flush draw and a straight draw a free card — the same card that beats you on the turn. Slow-play a passive player who only bets made hands and the pot just dies: you check, they check, and your monster wins the minimum at showdown instead of a stack. The board and the opponent decide this, not the strength of your hand alone.