Original: Codes are usually reserved for former countries, overseas territories, international organizations, and special nationality status (for their respective reserved codes, see the sections Reserved code elements in ISO 3166-1 alpha-2 and ISO 3166-1 alpha-3; there are no reserved numeric codes in ISO 3166-1).
Simplified: Usually, obsolete codes may be kept as reserved, while some overseas territories, international organizations, and special nationality status have reserved codes of their own. See the corresponding sections in ISO 3166-1 alpha-2 and ISO 3166-1 alpha-3 for their respective reserved codes (ISO 3166-1 numeric does not have reserved codes).