A sum of money due by certain and express agreement; as by bond for a determinate sum, a bill or note, a speclal bar-gain, or a rent reserved on a lease, where the amount is fixed and specific, and does not depend upon any subsequent valuation to settle It 3 Bl. Comm. 154; Camden v. Allen, 26 N. J. Law, 398; Appeal of City of Erie, 91 Pa. 398; Dickey v. Leonard, 77 Ga. 151; Hagar v. Reclamation Dist, 111 U. S. 701, 4 Sup. Ct. 663, 28 L. Ed. 569; Appeal Tax Court v. Rice, 50 Md. 302