preempt
a bid whose primary objectives are to interfere with opponents’ ability to bid to their best contract, with some safety, and to fully describe one’s hand to one’s partner in a single bid.
A preemptive bid is usually made by jumping, i.e. skipping one or more bidding levels. Since it deprives the opponents of the bidding space, it is expected that they will either find a wrong contract (too high or in the wrong place) of their own, or fail to find any.