President Obama and Congressional Republicans are playing a high-stakes "game of chicken," but if the parties can't agree on a new federal spending plan by March 4, the government may very well shut down for the first time in 15 years. What exactly does that mean? Here, a brief guide:

What constitutes a "government shut-down"?

Without money to pay for them, federal services both large and small would be affected. Some veterans might not get benefit checks, people would not be able to apply for Social Security, and the State Department might not issue new passports, says Ed O'Keefe in The Washington Post. Government-run museums and national parks would also probably close.

Would anything stay open?

Yes. "Essential" services, like those tied to national security, would continue. And the president has "wide discretion" to determine which agencies should stay open. The U.S. Mint would still pump out currency, and the post office would still deliver mail.

Could "non-essential" federal employees work anyway?

In a word, no. There won't be money to pay them. And even if they wanted to work without pay, they could be subject to fines of up to $5,000 (or two years in prison) for violating a federal law that forbids volunteer labor, says O'Keefe in The Washington Post. Last time, some of the "frustrated feds" who weren't allowed to work "sought temporary jobs as bike messengers and waitresses in order to pay holiday bills."

What caused the last shutdown?

A similar budget battle. President Bill Clinton and the Congress led by Newt Gingrich clashed repeatedly over the spending plan, spurring two shutdowns. The first, in November, 1995, lasted five days and resulted in the furlough of 800,000 federal employees, according to a Congressional Research Service report. Then, after a temporary budget agreement expired the following month, the government shut down again from Dec. 16, 1995, to Jan. 6, 1996 — the longest closure in U.S. history.

How bad was it?

Payments to more than 400,000 veterans were delayed, as was the processing of Medicare and Social Security checks, though they were eventually sent out. The CDC "stopped their disease surveillance programs," new patients were not accepted into health research studies, and clean-up work at 609 toxic waste sites stopped, says David Corn at Politics Daily. Oh, and elephant manure piled up in a National Zoo parking lot because government workers couldn't ship it away for composting.

Will history repeat itself?

It's certainly possible, and federal agencies have reportedly told senior officials to get ready for a shutdown. There's still time to reach a compromise, but there remains a big gap between the budget demands of Republicans and Democrats. And if they can't agree, says Frank James at NPR, a shutdown means "a lot of economic pain at a time when a lot of people are already hurting."

Sources: Congressional Research Service, New York Daily News, Politics Daily, The Washington Post, NPR