When there is a spending budget of about $3.318 trillion, and projected revenues around $3.034 trillion you will have a deficit. A deficit is when federal outlays are more than federal receipts.
Outlays are actual monies spent in any given fiscal year, such as that $3.318 trillion in fiscal year 2013-2014.
Receipts are revenues received or projected to be received in. For example, any inflow of funds to the U.S. Treasure such as corporate taxes, payroll taxes and individual taxes as well as, user fees are considered receipts.
So back to the original thought, when there is more money going out than there is coming in, you have a deficit.
Government Money Printing
The government is trying to solve its deficit problem by printing more money. However, by doing so all they are doing is driving the value of the dollar down. When you double the amount of money (supply) it is now worth half the value. This is especially more so now that the dollar is no longer backed by gold! Thus, we now have a devalued dollar.