The debt ceiling, in simple terms, is the maximum amount of money the United States can borrow in order to pay its existing obligations. The debt ceiling (or limit) when raised does not allow for new expenditures, but instead allows the government to pay for programs it has already committed to paying for. Historically, raising the debt limit was done quickly and without contention, as the debt limit was seen as a financial necessity and not as political capital. Since the 1960, Congress has raised, extended or revised the debt limit a total of 78 times, and up until recently it was not used as leverage.
Currently, the United States is set to hit the debt ceiling on May 19, 2013. The country was set to hit the limit sometime in early February, but Congress passed a three-month extension of the debt ceiling so as to not have the issue of sequestration, an expiring continuing resolution, and the debt ceiling come up within a matter of weeks.