Supplemental Appropriation: An act appropriating funds in addition to those in the 13 regular annual appropriations acts. Supplemental appropriations provide additional budget authority beyond the original estimates for programs or activities (including new programs authorized after the date of the original appropriation act) in cases where the need for funds is too urgent to be postponed until enactment of the next regular appropriation bill. (See Appropriation Act.)

[The Congressional Budget Process: An Explanation, Appendix J (Glossary), Committee on the Budget of the U.S. Senate, S. Prt. 105-67 (Revised December 1998).]