A bond generally have two main maturity structures:
Bullet Maturity - Most corporate and government bonds use this structure, which requires the borrower to pay the investor one lump sum of the principle on the stated maturity date.
Amortizing Securities - Asset-Backed Securities (ABSs) along with Mortgage Backed Securities (MBSs) have structures that pay the principal back at certain intervals during the bond's life. For example, a mortgage payment includes part principle and part interest. They are called amortizing securities because the principle amount shrinks as the security matures, so that the last payment made to the investors closes out the issuer's responsibility concerning this bond