Uses and Applications
The ISO 3166-1 alpha-3 codes are used most prominently in ISO/IEC 7501-1 for machine-readable passports, as standardized by the International Civil Aviation Organization, with a number of additional codes for special passports; some of these codes are currently reserved and not used at the present stage in ISO 3166-1.
The United Nations uses a combination of ISO 3166-1 alpha-2 and alpha-3 codes, along with codes that pre-date the creation of ISO 3166, for international vehicle registration codes, which are codes used to identify the issuing country of a vehicle registration plate; some of these codes are currently indeterminately reserved in ISO 3166-1.
Read more about this topic: ISO 3166-1 Alpha-3