(A) “The term "budget authority" in general, means the authority provided by Federal law to incur financial obligations, as follows:
(i) provisions of law that make funds available for obligation and expenditure (other than borrowing authority), including the authority to obligate and expend the proceeds of offsetting receipts and collections;
(ii) borrowing authority, which means authority granted to a Federal entity to borrow and obligate and expend the borrowed funds, including through the issuance of promissory notes or other monetary credits;
(iii) contract authority, which means the making of funds available for obligation but not for expenditure; and
(iv) offsetting receipts and collections as negative budget authority, and the reduction thereof as positive budget authority.
(B) Limitations on budget authority. With respect to the Federal Hospital Insurance Trust Fund, the Supplementary Medical Insurance Trust Fund, the Unemployment Trust Fund, and the railroad retirement account, any amount that is precluded from obligation in a fiscal year by a provision of law (such as a limitation or a benefit formula) shall not be budget authority in that year.” (2 USCS § 622)