A note or bond whose coupons are based on the difference between two floating-rate indexes. Typically, these notes or bonds pay an above-market fixed-rate coupon for a specific period of time. Thereafter, these instruments will pay either the above-market fixed coupon or nothing, depending on whether the difference remains above a preset level or not. For example, a bond may be the following coupons:

This note or bond is often callable, where the issuer has the right to recall them after a specific number of years and every regular period thereafter (quarterly, semiannually, etc)