A government shutdown occurs when a government discontinues providing services that are not considered "essential." Typically, essential services include police, fire fighting, armed forces, and corrections.
A shutdown can occur when a legislative body (including the legislative power of veto by the executive) cannot agree on a budget financing its government programs for a pending fiscal year. In the absence of appropriated funds, the government discontinues providing non-essential services at the beginning of the affected fiscal year. Government employees who provide essential services, often referred to as "essential employees", are required to continue working.
Notable government shutdowns in the United States
Note that in the list of "essential" services above, police and firefighting are largely state and/or locally funded, so are not an issue in federal shutdowns.
↑ BUDGET MESS HITS CULTURAL GROUPS, The Buffalo News, Feb. 7, 2005; COUNTY LEADERS BRACE FOR CLOSINGS, The Buffalo News, Feb. 21, 2005; SERVICES SHUT DOWN AS COUNTY FAILS TO PAY UP, The Buffalo News, Jul. 3, 2005