A security agreement is a legal document that outlines the terms of a loan or other financial arrangement. It is also known as a LIEN, which is a four-letter word that is often used in crossword puzzles. A LIEN is a form of security interest granted over an item of property to secure the payment of a debt or performance of some other obligation. The LIEN gives the holder of the LIEN the right to take possession of the property if the debt is not paid or the obligation is not fulfilled.