What Is a merchants promise to leave an offer open called?

A merchant's promise to leave an offer open is called a "firm offer." This term is often used in the context of the Uniform Commercial Code (UCC), which allows merchants to make a written offer that remains open for a specified period, during which the offer cannot be revoked. A firm offer must be in writing and signed by the merchant, ensuring that the offeree can rely on the offer for the duration specified.