Which of the following terms describes an agreement lacking a formal written record?

The term "informal" accurately describes an agreement that lacks a formal written record. An informal agreement can occur in various contexts, often characterized by verbal communication and an understanding between the parties involved without any documentation to outline the specifics. This type of agreement is typically more flexible and may rely on trust rather than legal enforceability, which is crucial in the context of real estate transactions.

The other terms presented don't fit the definition of lacking a formal written record. "Executed" refers to an agreement that has been signed and completed, meaning it does have a formal record. "Bilateral" describes an agreement involving two parties with mutual obligations, but does not directly relate to the format of the agreement itself. Therefore, "informal" is the most appropriate term for an agreement that does not have any formal written documentation.