In Tetris, misplacing a tetrad in a way that causes large gaps beneath said tetrad, usually caused by dropping the peice before checking to make sure it is aligned properly, or by not having enough time to manipulate the peice before it falls. Technically it is a verb, but can easily be used as a noun.
"You're near the top of the screen. Be careful you don't donk."
Donk and its variants, short for Donkey, or stupid play, particularly putting (or donating) lots of chips into a hopeless pot. Occasionally used when someone makes a hand on the river and 'bad beats' another player.