A mortgage is the transfer of an interest in property (or in law the equivalent - a charge) to a lender as a security for a debt - usually a loan of money. While a mortgage in itself is not a debt, it is lender's security for a debt. It is a transfer of an interest in land (or the equivalent), from the owner to the mortgage lender, on the condition that this interest will be returned to the owner of the real estate when the terms of the mortgage have been satisfied or performed. In other words, the mortgage is a security for the loan that the lender makes to the borrower.

The term comes from the Old French "dead pledge," apparently meaning that the pledge ends (dies) either when the obligation is fulfilled or the property is taken through foreclosure.

In most jurisdictions mortgages are strongly associated with loans secured on real estate rather than other property (such as ships) and in some jurisdictions only land may be mortgaged. Arranging a mortgage is seen as the standard method by which individuals and businesses can purchase residential and commercial real estate without the need to pay the full value immediately. See mortgage loan for residential mortgage lending, and commercial mortgage for lending against commercial property.

The measurement of a mortgage with regards to cost to the borrower can be measured by Annual Percentage Rate (APR) or many other formulas for true cost such as Lender Police Effective Annual Rate (LPEAR).

In many countries it is normal for home purchases to be funded by a mortgage. In countries where the demand for home ownership is highest, strong domestic markets have developed, notably in Spain, the United Kingdom, Australia and the United States.

Participants and variant terminology

Legal systems, while having some concepts in common, employ different terminology. However, in general, a mortgage of property involves the following parties.

Mortgage lender

Mortgagee is the legal term for the mortgage lender. The main function of the mortgage is to provide security to the lender. Given the large sum of money involved in financing a property, a mortgage lender will usually want security for the loan that will provide a claim upon that security and will take precedence over other creditors. A mortgage accomplishes this security.

The lender loans the money and registers the mortgage against the title to the property. The borrower gives the lender the mortgage as security for the loan, receives the funds, makes the required payments and maintains possession of the property. The borrower has the right to have the mortgage discharged from the title once the debt is paid. If the mortgagor fails to repay the loan according to the conditions set forth by the lender, then the mortgagee reserves the right to foreclose on the property.

Borrower

Mortgagor is the legal term for the borrower, who owes the obligation secured by the mortgage, and may be multiple parties. Generally, the debtor must meet the conditions of the underlying loan or other obligation and the conditions of the mortgage. Otherwise, the debtor usually runs the risk of foreclosure of the mortgage by the creditor to recover the debt. Typically the debtors will be the individual home-owners, landlords or businesses who are purchasing their property by way of a loan.