A mortgage is the transfer of an interest in property (or the equivalent in law - 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 the 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 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 on other property (such as ships) and in some jurisdictions only land may be mortgaged. A mortgage is the standard method by which individuals and businesses can purchase real estate without the need to pay the full value immediately from their own resources. See mortgage loan for residential mortgage lending, and commercial mortgage for lending against commercial property.

The cost to the borrower is measured by the annual percentage rate (APR), which is an effective annual rate of interest and fees paid by the borrower.

Mortgage lender
Mortgagee is a party to whom property is mortgaged, usually a lender. Mortgage provides 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 with 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 a party who mortgages property. A mortgagor owes the obligation secured by the mortgage. 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.

Most buyers of real property would have difficulty saving enough money to make an outright purchase of real estate. The use of debt increases a buyer’s ability to buy through a combination of down payment and debt. As a result a real estate transaction seldom occurs without buyers relying on borrowed funds.
Borrowing for investment purposes
Aside from the absence of large amount of available money, there are several reasons why an investor (including a buyer of real estate) might borrow funds. Some of these include:

To diversify investments and reduce overall risk by using only part of the available funds for any one investment. However the mortgage loan enables him to purchase more assets than he would otherwise been able to, and therefore in general increases investment risk rather than reducing it.
To invest the borrowed funds at a higher rate of interest (yield) than the borrowing rate; for example, a sum is borrowed at an annual interest rate of 7% per year and used to invest in a project that returns 10% per year. This is likely to be speculative and there is usually a possibility that the project may turn out to return less than 7% per year or to lose money.
To free up equity for other purposes; for example, a commercial enterprise may prefer to use funds to purchase inventory or equipment instead of investing only in land and buildings.
To obtain a tax benefit. In some countries (such as Canada), mortgage interest is not tax deductible, but loans made for investment purposes are.

Other participants
Because of the complicated legal exchange, or conveyance, of the property, one or both of the main participants are likely to require legal representation. The terminology varies with legal jurisdiction; see lawyer, solicitor and conveyancer.

Because of the complex nature of many markets the debtor may approach a mortgage broker or financial adviser to help them source an appropriate creditor, typically by finding the most competitive loan.

The debt is, in civil law jurisdictions, referred to as hypothecation, which may make use of the services of a hypothecary to assist in the hypothecation.