A contract is a written or oral agreement between two or more parties or entities involved in a deal or transaction that is legally binding. The definition of a contract in California is a legally binding agreement negotiated between parties.An Irvine business lawyer can help with contracts. It should detail the work, price, when payments will be made. By definition, a contract is an agreement between two or more parties that a court will enforce. Legal purpose: The purpose of the agreement must not break the law. A judge can't enforce a contract to do something illegal, like sell illegal drugs. There are four elements to make a California contract valid. It is essential to the existence of a contract that there should be: 1. Parties capable of contracting; 2.