GAO Glossary of Terms and Definitions (September 2005)
A sum (1) that is received by an agency as a payment for commodities sold or services furnished either to the public or to another government account and (2) that is authorized by law to be credited directly to specific appropriation and fund accounts. Reimbursements between two accounts for goods or services are usually expenditure transactions/transfers.
Anticipated reimbursements are, in the case of transactions with the public, estimated collections of expected advances to be received or expected reimbursements to be earned. In transactions between government accounts, anticipated reimbursements consist of orders expected to be received for which no orders have been accepted. Agencies cannot obligate against anticipated reimbursements without specific statutory authority. (See also Offsetting Collections under Collections; Unfilled Customer Orders.)