A mortgage is a written pledge for the repayment of a loan using real property as security. The property you purchase is the collateral for the mortgage. If you fail to make payments on the loan, the lender can repossess your home. Mortgage loans are usually fully amortizing, which means that the monthly principal and interest payemnt will pay off the loan in the number of payments stipulated on the note.  Mortgage loans are also described by the length of time for repayment - 15, 30, and whether the interest rate is fixed or adjustable.  With amortization, your monthly payments are largely interest during the early years and principal later.