Debt of the United States
The United States public debt is the money borrowed by the federal government of the United States at any one time through the issue of securities by the Treasury and other federal government agencies. The US national public debt consists of two components:
Debt held by the public comprises securities held by investors outside the federal government, including that held by investors, the Federal Reserve System and foreign, state and local governments.
Intragovernment debt comprises Treasury securities held in accounts administered by the federal government, such as the Social Security Trust Fund. (Source: Wikipedia).