Which of the following is NOT a key element of a valid contract?

A valid contract must include several key elements to ensure its enforceability. Acceptance refers to the agreement between parties on the terms of the contract, which indicates a mutual understanding and agreement. Consideration involves the value exchanged between parties, which is essential for establishing a binding agreement. Capacity pertains to each party's legal ability to enter into a contract, which means they must be of legal age and sound mind.

Open-ended terms, however, can undermine the validity of a contract. A contract should have clear and definite terms so that all parties understand their rights and obligations. When terms are vague or not well-defined, it can lead to misunderstandings and disputes, making it difficult to enforce the contract. Therefore, the absence of specific and unambiguous terms is why open-ended terms do not qualify as a key element of a valid contract.