A fixed income security is one designed to pay interest/coupon payments on a predetermined basis, or a fixed schedule.
Fixed income securities are often used by late stage retirees who need safe, reliable income streams. Fixed income securities still have risk, such as interest rate risk where if interest rates rise the price of a fixed income security can fall.
Examples of fixed income securities are U.S. Treasuries, municipal bonds, or CDs. Because fixed income products carry relatively low risk, it generally translates into relatively lower returns.