Final answer:
A budget surplus occurs when government tax revenues exceed its spending, unlike a budget deficit, which happens when spending surpasses tax revenues. In 2009, the US experienced a significant budget deficit, underscoring what a surplus is not.
Step-by-step explanation:
Budget surpluses exist when government tax revenues exceed its spending. This means that the government has received more money from taxes than what it has spent over a specific period of time. A surplus is the opposite of a budget deficit, which occurs when government spending exceeds tax revenues. When government spending and taxes are equal, the government is said to have a balanced budget. For instance, the U.S. government ran a very large budget deficit in 2009, where it spent approximately $1.4 trillion more than the tax revenues collected, which was about 10% of the U.S. GDP for that year, illustrating a situation far removed from a surplus.