What are ISO country codes?
ISO country codes are standardized two letter codes assigned to each country and used by the Internet Assigned Numbers Authority (IANA) to create country code top-level domains (ccTLDs). Specifically, it is the ISO 3166-1 alpha-2 codes that were used to create the ccTLDs delegated and in use today.
ISO stands for International Organization for Standardization. The organization has been setting proprietary, industrial, and commercial standards for the world since 1947. ISO 3166-1 refers to standardized codes created for the names of countries and alpha-2 specifically refers to two letter codes (there were also three letter codes and numeric codes created under ISO 3166-1).
Please note that there are a few ccTLDs that do not use their country's ISO 3166-1 alpha-2 code. One example is .UK, as the United Kingdom's ISO country code is GB.