A bond investor buys a debt instrument, which is essentially a loan to a corporation or government. In exchange for this money, the bond investor receives an interest rate. Bonds pay at fixed intervals and for a fixed period of time and are therefore called “fixed-income securities.” The interest rate that the issuer pays is called a “coupon.” At maturity, the full amount of capital is returned to the investor. The two main criteria of bond investors for buying a debt instrument are duration and credit quality. Duration represents the length of the investment; credit quality is how strong the borrower is and how able they are to repay the full amount of debt.