What a party is required to give up under the terms of a contract. Both sides must have consideration in order for a contract to be valid and enforceable. For example, A and B agree that A will walk B’s dog for $10. A’s consideration is the $10 that A is giving; B’s consideration is the time B is giving up time to walk the dog. But if, instead, the agreement was only the A gives B $10, and B is not required to do anything, then they do not have an enforceable contract because B has no consideration.