A government shutdown happens when nonessential U.S. government offices can no longer remain open due to a lack of funding. The lack of funding usually occurs when there is a delay in the approval of the federal budget that will finance the government for the upcoming fiscal year. The shutdown remains in effect until funding legislation is passed.
During a government shutdown, many federally run operations will halt. Some organizations may still stay open by running on cash reserves, but once these funds run out, they will also close.