Assuming you're talking about properties in Western Washington (98383) and specifically a property listing in the NWMLS, then this presents a good example of why agents from Florida should not be answering the question. They probably should not be answering if you're asking about Alaska either, but I don't know that.
To answer your question, in the NWMLS it means that the sale is contingent on the buyer being able to sell their existing house. You can put another offer in on the property, and if that offer is enticing to the seller, they will give the original buyer notice of your offer, and that original buyer will have a limited time (default 5 days) to decide whether or not to waive their contingency. If they don't waive their contingency, then their contract terminates and yours will proceed.