The donkey is a player who makes unprofitable movements, is a player who does not know about numbers, makes bluffs meaningless, makes them when he should not do them.
They often do mini bet to try to see a turn and a cheap river, in
freerolls and micro limits it may work for them, but at higher levels it doesn't, that's where the term
donkbet comes from,
And as one partner said above, they are very dangerous players.
Unlike the agro player, against these players you must place strong bets, one two and three streets.
Do not try
bluffing against them, because they can pay with a third pair.
Guess what color I have to that kind of players.