A mortgage is a security interest in real property held by a lender as a security for a debt, usually a loan of money. 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.

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.

Foreclosure is the legal process by which a mortgagee, or other lien holder, usually a lender, obtains a court ordered termination of a mortgagor's equitable right of redemption. Usually a lender obtains a security interest from a borrower who mortgages or pledges an asset like a house to secure the loan. If the borrower defaults and the lender tries to repossess the property, courts of equity can grant the borrower the equitable right of redemption if the borrower repays the debt. While this equitable right exists, the lender cannot be sure that it can successfully repossess the property, thus the lender seeks to foreclose the equitable right of redemption. Other lien holders can also foreclose the owner's right of redemption for other debts, such as for overdue taxes, unpaid contractors' bills or overdue homeowners' association dues or assessments.

The foreclosure process as applied to residential mortgage loans is a bank or other secured creditor selling or repossessing a parcel of real property (immovable property) after the owner has failed to comply with an agreement between the lender and borrower called a "mortgage" or "deed of trust". Commonly, the violation of the mortgage is a default in payment of a promissory note, secured by a lien on the property. When the process is complete, the lender can sell the property and keep the proceeds to pay off its mortgage and any legal costs, and it is typically said that "the lender has foreclosed its mortgage or lien". If the promissory note was made with a recourse clause then if the sale does not bring enough to pay the existing balance of principal and fees the mortgagee can file a claim for a deficiency judgment.