Definition of Unilateral Contract: Contract in which only one party is required to do something. Explanation of Unilateral Contract: A unilateral contract is an agreement in which one party performs a specific act, typically in exchange for money. Unlike a bilateral contract, a unilateral contract only contains a promisor. For example, in a nonexclusive real estate listing, an agent does not enter into an agreement with a seller unless he or she finds an appropriate buyer first.