A nil bid is a high risk, high reward mechanic and is essentially a bid of zero. A player who places a nil bid must not win any tricks. if they succeed, their team will receive 100 points at the end of the round. If they fail, a penalty of -100 points will be given instead.
Your partner is an essential part of a nil bid as they can cover any high cards that you have that could result in you winning a trick and thus failing to meet your bid.