Definition of donkbet
A donkbet is a bet that we make out of position when we do not have the initiative (we bet before the player who has the initiative has had time to make his cbet). We could also call it "lead without the initiative". The donkbet refers to the "donkey bet". By donkey, we mean a fish, a pigeon, a bad player. Donkbets are, as the name suggests, a bet that bad players are more likely to make. Traditionally, without the initiative, the player who raised preflop is called when a flop is seen. Since he raised preflop, he should theoretically have the stronger hand (which explains the convention).
The donkbet, is it good or not?
If you make a donkbet, many players will raise you. It's a way for them to tell you "Your bet looks like a bluff, I'm the one with the initiative and I'm the one who showed strength before the flop, so you should fold". When you donkbet, you have to know what you are doing. It's a risky play because our opponent's range is not captured and we are out of position. In short, if you are going to donkbet, have a reason in mind because you are likely to get a hard time!