Final answer:
A lien theory state is when a borrower retains title to the real property used as security for a debt.
Step-by-step explanation:
A state in which a borrower retains title to the real property pledged as security for a debt is a lien theory state. This means that even though the borrower has given a lien on the property, they still hold the legal title to it. In contrast, in a title theory state, the lender holds the legal title until the debt is fully paid.