country code definition networking, standard
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).