A contract that is not valid due to its nature but has been acted upon can be referred to as?

In the context of contract law, a contract that is inherently invalid due to its nature but has been acted upon can be referred to as voidable. Voidable contracts are those agreements that are valid and enforceable until one party chooses to enforce or void it. They often arise from certain conditions such as misrepresentation, undue influence, or lack of capacity, which allow one party to later invalidate the agreement. However, if such a contract has been acted upon—meaning at least one party has begun to perform their obligations under the contract—it demonstrates that the involved parties may have initially treated the agreement as valid, thereby giving rise to certain rights and duties.

The other options do not accurately capture the essence of this situation. An implied contract refers to agreements that are established by actions or circumstances rather than written or spoken words. An executed contract is one in which all parties have fulfilled their obligations; a voidable contract, by contrast, still has the potential to be voided by one party. A unilateral contract involves one party making a promise in exchange for the act of another party rather than a mutual exchange of promises, which does not apply to the scenario described in the question.