Security Agreement
  
A secured debt involves a loan that is backed by some asset. There is collatoral or a lien involved, so that, if a default happens, the lender has recourse to get the debt repaid. Otherwise, the debt is unsecured...which means that, in a situation where the borrower skips town and refuses to pay, the lender is screwed.
The security agreement is the document that details the secured debt. It lays out the terms of repayment and specifies the collateral involved. It presents the situations where the lender can seize the property and any other details related to the situation.