The national debt has grown significantly in recent years due to rising annual deficits. A deficit occurs in any year the government spends more money than it takes in. Borrowing to make up the difference is added to the national debt -- technically referred to as the gross federal debt.

The gross debt has two components: 1) Debt held by the public -- money the government borrows on the open market from domestic or foreign investors; and 2) Intra-governmental debt -- money the government owes itself, as in the Social Security trust fund.