Wiktionary
serial bond
n. (context legal English) Bonds issued in a series by a public entity that are payable at different times.
Wikipedia
Serial bond
Serial bonds are financial bonds that mature in installments over a period of time. In effect, a $100,000, 5-year serial bond would mature in a $20,000 annuity over a 5-year interval. Bond issues consisting of a series of blocks of securities maturing in sequence, the coupon rate can be different.