The percentage rate at which The cost you pay to borrow money. It is the payment you make to a lender for the money it has loaned to you. Interest is usually expressed as a percentage of the amount borrowed. accumulates or increases on a A loan using your home as collateral. In some states, the term mortgage is also used to describe the document you sign (to grant the lender a lien on your home). It also may be used to indicate the amount of money you borrow, with interest, to purchase your house. The amount of your mortgage often is the purchase price... loan.