International Organization for Standardization Definition. The International Organization for Standardization, or "ISO", is the international standard setting body composed of representatives from various national standards organizations, which determines, among other things, the currency codes used by forex traders, such as GBP for the British Pound. ISO 4217 is the international standard describing these three-letter codes, which define the names of currencies established by the International Organization for Standardization (ISO). The ISO 4217 code list is the established norm in banking and business all over the world for defining different currencies, and in many countries the codes for the more common currencies are so well known publicly, that exchange rates published in newspapers or posted in banks use only these to define the different currencies, instead of translated currency names or ambiguous currency symbols. The first two letters of the code are the two letters of ISO 3166-1 alpha-2 country codes, which are also used as the basis for national top-level domains on the Internet, and the third is usually the initial of the currency itself. For example, Japan‘s currency code is JPY-JP for Japan and Y for yen. Also, if a currency is revalued, the currency code‘s last letter is changed to distinguish it from the old currency. There is also a three-digit code number assigned to each currency, in the same manner as there is also a three-digit code number assigned to each country as part of ISO 3166.