Explanation:

- Option 1: An agreement enforceable by law

This is the correct definition. A contract is a legal agreement that can be enforced in a court.

- Option 2: A set of promises

While contracts often contain promises, just making promises doesn’t make something a contract unless it’s enforceable by law.

- Option 3: An agreement not enforceable by law

This describes a void agreement, not a contract. If it can’t be enforced by law, it’s not a contract.

- Option 4: A promise to do something or abstain from doing something

This is the idea behind a contract (offer and acceptance), but without legal enforceability, it doesn’t qualify as a contract.