In the Federal budget, a means of presenting budget authority, outlay, and tax expenditure data in terms of the principal purposes which Federal programs are intended to serve. Each specific account is generally placed in the single function (e.g., national defense, health) that best represents its major purpose, regardless of the agency administering the program. The Congressional Budget and Impoundment Control Act of 1974 requires the Congress to estimate outlays, budget authority, and tax expenditures for each function. Functions are subdivided into narrower categories called sub-functions.