Float

Calling a bet — usually a flop continuation bet — with a hand that is probably behind, planning to take the pot away on the turn or river when the opponent gives up.

Against an opponent who bets flops automatically and gives up on turns, and when you have position, so you can see them check before deciding. Out of position the play mostly fails: you have to act first and they can simply bet again.

Something with a little equity as a backup — a backdoor draw, an overcard, a gutshot — and ideally a blocker to their strongest hands. Floating with pure air works against the right opponent but leaves you nothing when they keep betting.