When one party owes money to another, the lender may ask the debtor for security on the debt. In a mortgage, the debtor (mortgagor) transfers legal title to his real property to the lender (mortgagee), and the mortgagee will hold that title until the grantor pays off the debt in its entirety.
In roughly half of U.S. jurisdictions, the law considers a mortgage a lien (a security interest only), and the mortgagor retains the right to usage of the property until he defaults on the debt. However, many states find that a mortgage is an actual ownership interest, which gives the mortgagee all rights over the property.
Transfer of Mortgage
Should a mortgagor decide to sell the property, the mortgage remains on the land. However, the mortgagor will remain personally liable for the debt secured by the mortgage, unless the new owner of the property assumes the mortgage and thus becomes primarily liable for the debt.