ISO standard 3166-1 gives codes for countries, dependent
territories, and special areas of geographic interest.
The ISO 3166-1 alpha-2 code is a two-letter code. In most cases,
this two-letter code is used as the top-level domain for that
country on the Internet. The only exception is that the United
Kingdom uses ".uk" instead of its ISO 3166-1 alpha-2 code of GB.
The ISO 3166-1 alpha-2 code is also used as the first two letters
of each currency code, including GBP for UK pounds sterling.
The ISO 3166-1 alpha-3 code is a three-letter code.
The ISO 3166-1 numberic code is a number associated with each
country or territory in the standard.