The following is excerpted from an online document produced by the U.S. Census Bureau pertaining to voting districts (found at <http://www.census.gov/geo/www/cob/vt_metadata.html>):

"Voting district (VTD) is the generic name for geographic entities, such as precincts, wards, and election districts, established by state, local, and tribal governments for the purpose of conducting elections. States participating in the Census 2000 Redistricting Data Program as part of Public Law 94-171 (1975) may provide boundaries, codes, and names for their VTDs to the U.S. Census Bureau. The U.S. Census Bureau first reported data for VTDs following the 1980 census. Because the U.S. Census Bureau requires that VTDs follow boundaries of census blocks, participating states often adjusted the boundaries of the VTDs they submit for data tabulation purposes to conform to census block boundaries. If requested by the participating state, the U.S. Census Bureau identifies these "adjusted" VTDs as "pseudo-VTDs."

For Census 2000, each VTD is identified by a one- to six-character alphanumeric census code that is unique within county. The code "ZZZZZZ" identifies parts of a county in which no VTDs were identified."