Definition - Noun 1 a: the act or fact of agreeing <by mutual ~> b: unity of opinion, understanding, or intent esp : the mutual assent of contracting parties to the same terms <if they reach ~> Under common law, agreement is a necessary element of a valid contract. Under Uniform Commercial Code section 1-201(3), agreement is the bargain of the contracting parties as represented explicitly by their language or implicitly by other circumstances (as a course of dealings). 2 a: an expression (as a settlement, covenant, or contract) of the intent or willingness of two or more parties to bind at least one to terms usu. determined by negotiation <an ~ must be sufficiently definite before a court can enforce it J. D. Calamari and J. M. Perillo> b: the language or instrument embodying such an expression <signed the ~>