**ISO 3166** is the international standard that assigns two-letter, three-letter and numeric codes to the countries, territories and subdivisions of the world. The two-letter alpha-2 codes (such as FR for France, JP for Japan) are widely used as identifiers for national flags in databases, URLs and filenames. ISO 3166-2 codes extend the system to subdivisions such as states, provinces and overseas territories.
**Example**: The flag of Japan is commonly indexed under the ISO 3166-1 alpha-2 code JP, and its image filenames often follow the form jp.svg or jp.png.
**See also**: [fiav](/glossary/fiav/), [vexillology](/glossary/vexillology/), [hex](/glossary/hex/), [construction-sheet](/glossary/construction-sheet/)