ISO 3166-1 Alpha-3

ISO 3166-1 alpha-3 codes are three-letter country codes defined in ISO 3166-1, part of the ISO 3166 standard published by the International Organization for Standardization (ISO), to represent countries, dependent territories, and special areas of geographical interest. They allow a better visual association between the codes and the country names than the two-letter alpha-2 codes (the third set of codes is numeric and hence offers no visual association). They were first included as part of the ISO 3166 standard in its first edition in 1974.

Read more about ISO 3166-1 Alpha-3:  Uses and Applications, Deleted Codes