I always thought a donk bet was leading out into a preflop raiser with a retardly small bet. (min-bet or tiny fraction of the pot) In these cases, the name is truly deserved, as it makes zero sense.
By the way, this seems to be the norm at 25NL. Every time I bet preflop and get multiple callers, some donk comes out firing with a 1/5th of the pot bet, and almost always folds to a reraise. I could see its use as a collusion tool in multi-way pots, but other than that, it seems like a good way to burn money.