A legal document, usually in writing, giving details of a formal legally binding agreement, between two or more different people or groups. To be legally binding it must contain certain elements: it must contain an offer made by one party and accepted in its entirety by the other, it must include some form of consideration whether it be money, goods or services, and it must be properly signed by all parties to it, and dated.

Sometimes known as a repudiatory breach, is a breach of an essential part of a contract that it permits the distressed party to terminate performance of the contract, in addition to entitling that party to sue for damages.