Debt instruments are contracts where one party lends money to another with predetermined interest rates and repayment terms. Principal features of bonds include maturity date, term to maturity, coupon rate, and principal amount. Bonds can be further classified by term as short, medium, or long-term. Coupon payments and other features like term to maturity can be modified, for example through zero coupon bonds, floating rate bonds, callable bonds, and convertible bonds. Principal repayment can also be modified, such as through amortizing bonds or bonds with sinking fund provisions.