n. an agreement in which the parties exchange promises for each to do something in the future. "Susette Seller promises to sell her house to Bobby Buyer and Buyer promises to pay Seller $100,000 for it." This is distinct from a "unilateral contract," in which there is a promise to pay if the other party chooses to do something. "I'll pay you $1,000 if you'll stop smoking." These are basically academic differences which are only important in the rare instance in which one person has acted in anticipation that the other will have obligations as well.