The total amount owed by a national government. The US debt was $4.84 trillion dollars at the end of fiscal year 2006, not counting money owed by one federal agency to another. That’s roughly 36 per cent of the output of the entire US economy for that year. Generally, the debt rises each year by the amount of the Budget Deficit, or declines by the amount of the Budget Surplus. Information about the debt can be found at the website of the Bureau of the Public Debt, an arm of the US Treasury.
(A technical note: When speaking of the national debt, economists and news reporters generally mean only money the government owes to others, not to itself. Congress, however, has enacted a “Debt Limit” that applies to the combined total of the debt owed to outsiders, ttechnically called “debt held by the public," and to itself, termed "intergovernmental holdings." The latter is made up mostly of the Social Security and Medicare trust funds. The total of the two debts is the “total public debt outstanding.” That amount was $8.51 trillion as of the end of fiscal year 2006. The amount actually subject to the Debt Limit was somewhat less, $8.42 trillion, due to a variety of minor exceptions.)
U.S. Debt = http://www.publicdebt.treas.gov/opd/opds092006.htm