ISO country code can refer to

• ISO 3166-1 for countries that currently exist
  • ISO 3166-1 alpha-2
  • ISO 3166-1 alpha-3
  • ISO 3166-1 numeric
• ISO 3166-3 for countries that do not exist anymore

Generally, it's the two letter country code of ISO 3166-1 alpha-2.

It is not the same as ISO 3166 because ISO 3166-2 is not a country code.