Final answer:
The total money owed by the U.S. Treasury to holders of U.S. securities is known as the total public debt, which is an accumulation of budget deficits over the years minus any budget surpluses.
Step-by-step explanation:
The total amount of money owed by the United States Treasury to holders of U.S. securities is the total public debt. This includes all of the money borrowed to cover budget deficits over the years. When the government spends more than it earns in a given year, it runs a deficit, and to cover this, it borrows by issuing Treasury securities. Over time, the accumulation of these deficits, minus any budget surpluses, constitutes the national debt.
Historically, the U.S. took on debt primarily during wartime and worked to pay it down during peacetime. However, since the 1980s, considerable debt has been accumulated even in peacetime. Notably, the U.S. had a brief period of budget surpluses from 1998 to 2001, followed by annual budget deficits from 2002 onwards, with particularly large deficits during the recession of 2008 to 2009.
The budget surplus or deficit is measured annually, whereas total government debt or national debt is the sum of those figures over time. By the end of 2015, the country's debt had reached almost $19 trillion and by March 2021, the total debt amounted to $22 trillion.