GAO Glossary of Terms and Definitions (September 2005)
A system of classifying budget authority, outlays, receipts, and tax expenditures according to the national needs being addressed. Each concurrent resolution on the budget allocates budget authority and outlays among the various functions.
Each budget account appears in the single budget function (for example, national defense or health) that best reflects its major purpose, an important national need. A function may be divided into two or more subfunctions, depending upon the complexity of the national need addressed. (See also Budget Activity.)
(For a presentation of the functional classification for the fiscal 2006 budget, see app. IV. For a distinction, see Object Classification. See also Agency Mission; Budget Activity; Subfunction.)