A donkament refers to a tournament that attracts many weaker players, so-called donkeys, because of its structure and/or its buy-in. It is therefore called a donkey tournament or a donkament.
Such tournaments are usually characterised by rapidly increasing blind levels and a high number of weak, overly daring and irrational players, which makes it difficult or even impossible to play a strategically sensible game.
This is usually the case in freerolls. They don't require any buy-in, the participants have nothing to lose and therefore play rather randomly without thinking about their game too much. You will often see multi-way all-ins with the most ridiculous hands in the early phases of a freeroll.
Tournaments with a very low buy-in and turbo tournaments are also often affected by this phenomenon.