A mortgage is a device used to create a lien on real estate by contract. The mortgage is an instrument that the borrower (called the mortgagor) uses to pledge real property to the lender (called the mortgagee) as security for a debt, also called hypothecation.
The mortgage instrument contains two parts:
the mortgage, which is the pledge
the note, which is the actual evidence of the debt and promise to repay (sometimes called a promissory note).
To protect the lender, a mortgage is recorded in the public records creating a lien (when there are multiple liens, order of recording determines priority).
At common law, a mortgage was a conveyance that on its face was absolute and conveyed a fee simple estate, but which was in fact conditional, and would be of no effect if certain conditions were met --- usually, but not necessarily, the payment of a debt by the original landowner. Hence the word "mortgage," Law French for "dead pledge;" that is, it was absolute in form and in theory required no further steps to be taken by the creditor.
In many U. S. states, however, a mortgage has been converted by statute to a device for creating a security interest in land. When the landowner fails to perform on the obligation secured by the mortgage, the mortgage holder must file a foreclosure to cause the property to be sold at auction, usually by the sheriff. Since mortgage debt is often the largest debt owed by the debtor, banks and other mortgage lenders run title searches of the real property to make certain that the lien of the mortgage is prior to anyone else's claim