A class of debt security in which a portion of the underlying principal amount is paid in addition to periodic interest payments to the security's holder. The regular payment that the security holder receives is derived from the payments that the borrower makes in paying off the debt.   



|||Mortgage-backed securities (MBS) are one of the most common forms of amortizing security. With an MBS, the monthly mortgage payments that mortgagors make are pooled together and are then distributed to MBS holders. Depending on the way in which a security is structured, holders of these investments may be subject to prepayment risk, as it is not uncommon for the underlying borrower to prepay a portion, if not all, of the debt's principal. In the event that prepayment occurs, the investor will receive the rest of the principal and no more interest payments will occur.