A quick definition of legal consideration:

Legal consideration refers to something of value that is given or promised by one party in exchange for the promise of the other party. This can include an act, a forbearance, or a return promise. Consideration is necessary for an agreement to be enforceable. It must be fair and reasonable under the circumstances of the agreement, and it cannot be illegal or immoral. Past consideration, or something given, done, or suffered in the past, is not considered valid consideration. Valuable consideration is something that is of value to one or both parties, and it can involve gain or benefit to the promisor or loss or disadvantage to the promisee. In parliamentary law, consideration refers to the process by which a deliberative assembly disposes of a motion, including debate, amendment, and referral to a committee.