As described in FIPS Pub 6-4, an administrative division in the United States, just below the level of a State, given the same status as counties for information processing and statistical purposes (such as the U.S. Census), in places which do not have counties.

These include:

Louisiana Parishes
Alaska Boroughs and Census Areas
The District of Columbia
The independent cities of Maryland, Missouri, Nevada, and Virginia
Puerto Rico Municipios