While the debt can be measured in trillions of dollars, it is usually measured as a percentage of gross domestic product (GDP), the debt-to-GDP ratio. That's because as a country's economy grows, the amount of revenue a government can use to pay its debts grows as well.
In addition, a larger economy generally means the country's capital markets will grow and the government can tap them to issue more debt. This means that a country's ability to pay off debt, and the effect that debt might have on the country's economy, is dependent on how large the debt is as a proportion of the overall economy, not the dollar amount.
First, it's important to understand what the difference is between the federal government's annual budget deficit (also known as the fiscal deficit) and the outstanding federal debt, known in official accounting terminology as the national public debt. Simply explained, the federal government generates a budget deficit whenever it spends more money than it brings in through income-generating activities. These activities include individual, corporate, or excise taxes.
To operate in this manner of spending more than it earns, the U.S. Treasury Department must issue Treasury bills, notes, and bonds. These Treasury products finance the deficit by borrowing from the investors, both domestic and foreign. These Treasury securities also sell to corporations, financial institutions, and other governments around the world.3
By issuing these types of securities, the federal government can acquire the cash that it needs to provide governmental services. The national debt is simply the net accumulation of the federal government's annual budget deficits. It is the total amount of money that the U.S. federal government owes to its creditors. To make an analogy, fiscal or budget deficits are the trees, and the national debt is the forest. SOURCE: Inestopedia
