Donk bet
A flop bet by the player who only called before the flop, made before the action reaches the raiser. A move out of turn: the bet was not his to make.
A donk bet is a bet out of turn. The opponent raised before the flop, and by the logic of the game the flop bet is his to make. If instead you bet first, without waiting for his move, that is a donk. The name is dismissive because weak players do it most, and that is exactly why the move gets read: people bet out of turn not when they are confident but when the flop suited them.
A donk bet gets named and judged on its own, mine and the opponent's alike. Mine usually means I gave up a check-raise that would have earned more. His says more about his hand than any other bet: over eight sessions I was donk-bet into twice, both times by a made hand, and both times the money was mine to lose.
An example from session 8
K♠J♠ in the big blind against a button raise, flop J♣ 8♠ 8♥, two pair with the top kicker. I act first and bet myself, $2.75, without waiting for his bet. Turn: first again, $5.50. Two moves out of turn produced $8.25 in the pot, an opponent who had read me since the flop, and a river where he was the one betting. Minus $28.35 to A♠J♥, the same hand with an ace instead of a king.
The same in business
A move out of turn is read before it is heard. If you speak out of turn only when you are completely sure, the fact of speaking says everything about your position that you wanted to hide. Every word out of turn at a meeting is read the same way: if they are talking now, things are worse than we thought.
The whole hand is in session 8: “A move out of turn says something about you that you did not mean to say”.
The other terms are in the glossary.