An administrative county is an administrative area in the British Isles.
The term was introduced for England and Wales by the Local Government Act 1888, which created county councils for various areas, and called them 'administrative counties' to distinguish them from the traditional counties.
In England and Wales the legislation was repealed in 1974, and entities called 'counties' were introduced in their place. Though strictly inaccurate, these are often called 'administrative counties' to distinguish them from both the traditional counties, and the ceremonial counties.
In Scotland they were repealed in 1975 and replaced with a system of regions.
In Northern Ireland they were never formally repealed, though have been replaced for local government use by a system of 26 districts.
In Republic of Ireland the legislation that created them remained in force until the Local Government Act 2001 was passed, which renamed them 'counties'.
The administrative counties that did not share the names of traditional counties :
England
Scotland
Republic of Ireland
and, created in 1994 -
Technically, county boroughs were (and in the case of Northern Ireland, are) administrative counties in their own right, as were the counties of cities in Scotland.
See also: administrative counties of England, subdivisions of Wales, subdivisions of Scotland, counties of Ireland.