A mortgage is a loan secured by property, usually real estate property. Lenders define it as the money borrowed to pay for real estate. In essence, the lender helps the buyer pay the seller of a house, and the buyer agrees to repay the money borrowed over a period of time, usually 15 or 30 years in the U.S. Each month, a payment is made from buyer to lender. A portion of the monthly payment is called the principal, which is the original amount borrowed. The other portion is the interest, which is the cost paid to the lender for using the money. There may be an escrow account involved to cover the cost of property taxes and insurance.