Donk bet
A donk bet is a bet made out of position by the player who was not the aggressor on the previous street, so it takes the lead away from whoever had it.
The name is unkind and the play is not always bad. It became a term because beginners bet out with weak hands into the raiser, but a lead is a reasonable choice on boards that favour the caller, where the raiser would not have bet much anyway.
What makes it hard to do well is that it splits your range in two. Every hand you lead with is a hand you no longer have when you check, and if the leads are only your good hands, the checks become easy to attack.
an example
your cards
board
You called a raise from the big blind and flopped top pair. Leading for a third of the pot is not obviously wrong here: this board hits your calling range more often than the raiser range, and checking invites a bet you would rather have made yourself.
This example is made up. The real one is in your own hand history: find donk bet in your own hands and see how often it came up and what it cost you.
related terms
Probe bet
A probe bet is a bet made out of position on the turn or river after the previous aggressor declined to bet the street b ...
Out of position
You are out of position when you have to act before your opponent on every betting round after the flop, which means com ...
C-bet
A continuation bet, or c-bet, is a bet on the flop made by the player who raised last before the flop.
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Knowing the word is not the same as seeing it.
Forty hands against a bot, no account, and your own hand history at the end.