The Trust Funds of the Federal Government are distinctly different from conventional non-Federal trust funds and have no statutory definition that applies generally. As a general matter, Federal Trust Funds are accounting systems used to track the flow of streams of receipts ostensibly used for a dedicated purpose.
See the following summary for further information on the subject: What Are Federal Trust Funds?
Social Security Trust Funds
Medicare Trust Fund
Highway Trust Fund
Airport Trust Fund
Joint Committee on Taxation, Summary of Legislative Proposals Related to the Airport Trust Funds (April 15, 1980) See p. 8 for reference to H. Con. Res. 307 – Concurrent Resolution on the Budget for Fiscal Year 1981.
GAO Glossary of Terms and Definition (September 2005)
Trust Fund Accounts
See under Account in the President’s Budget.