What is the legal term for a contract that can be voided by one party due to a defect?

A contract that one party can void because of a legal defect is a voidable contract.

A voidable contract is initially valid and enforceable unless the legally protected party chooses to rescind it. The defect may involve circumstances such as fraud, duress, undue influence, misrepresentation, or one party’s lack of legal capacity. Depending on the defect and applicable law, the protected party may instead affirm the agreement and continue with it.

This differs from a void contract. A void contract is treated as having no legal effect from the outset, so neither party ordinarily needs to exercise a cancellation right. An agreement involving an illegal purpose is a common example. An unenforceable contract is different again: it may be valid in substance but cannot be enforced in court because of a rule such as a writing requirement or a limitation period.

“Executory contract” describes performance that remains due by one or both parties; it says nothing by itself about whether the agreement is defective or cancellable. The exact grounds and procedures for avoidance vary by jurisdiction.