Updated: Sep 30, 2021
A contract is a legally binding document between at least two parties that defines and governs the rights and duties of the parties to an agreement.
An agreement between private parties creating mutual obligations enforceable by law.
A mutual assent, expressed by a valid offer and acceptance.
A contract is legally enforceable because it meets the requirements and approval of the law. A contract typically involves the exchange of goods, services, money, or promise of those. "Breach of contract", means that the law will have to award the injured party either access to legal remedies such as damages (en.wikipedia.org)
A unilateral contract is one in which there is a promise to pay or give other consideration in return for actual performance. (I will pay you $500 to fix my car by Thursday; the performance is fixing the car by that date.)
A bilateral contract is one in which a promise is exchanged for a promise. (I promise to fix your car by Thursday and you promise to pay $500 on Thursday.)
Contracts can be either written or oral, but oral contracts are more difficult to prove and in most jurisdictions, the time to sue on the contract is shorter (such as two years for oral compared to four years for written). (dictionary.law.com)
Contract law is generally governed by the state Common Law, and while general overall contract law is common throughout the country, some specific court interpretations of a particular element of the Contract may vary between the states. (law.cornell.edu)