The Free On-line Dictionary of Computing (30 December 2018):

country code
ISO 3166

    Originally, a two-letter abbreviation
   for a particular country (or geographical region), generally
   used as a top-level domain.

   Originally country codes were just for countries; but country
   codes have been allocated for many areas (mostly islands) that
   aren't countries, such as Antarctica (aq), Christmas Island
   (cx) and Saint Pierre et Miquelon (pm).

   Country codes are defined in ISO 3166 and are used as the
   top level domain for Internet hostnames in most countries
   but hardly ever in the USA (code "us").  ISO 3166 defines
   short and full english and french names, two- and three-letter
   codes and a three-digit code for each country.

   There are also language codes.

   Latest list
(http://www.iso.org/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html).

   (2006-12-11)