Probe bet
Betting OOP after the aggressor declined to c-bet
Definition
A probe bet is a bet made out of position, on the turn or river, after the preflop aggressor checked the previous street instead of c-betting. The name says it all: probing a range that just showed weakness. Don't confuse it with a donk bet: the donk bets INTO the aggressor before they've acted on that street (betting the flop OOP after defending the BB, for instance). The probe strikes AFTER their surrender: by checking back the flop, the aggressor removed from their range most of the strong hands that would have c-bet — their range reaches the turn capped and weakened. So the probe fires at a high frequency, mixing thin value bets (pairs that beat their give-ups) with semi-bluffs (draws). It reclaims the initiative they abandoned and makes their inaction cost them — letting them check back and then see a free river would be a gift.
You defend the BB with 9♠8♠ against a BTN open. Flop T♠6♥2♦: checks through. Turn 7♣: you just hit the nut straight, and his flop check-back drained his range of its best hands. Probe two-thirds pot: his pairs and draws will pay, and almost nothing in his range can catch up.