Fixed Coupon on a Bond

Bonds pay interest twice a year—that interest is called a "coupon" because, in the good ol' days, people would clip the coupon from the bond, mail it in, and get a check from the bondholder a few weeks later. The coupon itself is "fixed" in that if, say, a $1,000 savings bond pays 4%, it'll pay a fixed coupon amount of $20, twice a year.