Issuer identification number (IIN) is the formal name for what the card industry usually calls a bank identification number (BIN). The BIN entry covers how these ranges are allocated, sponsored and used in routing; this page explains the standard behind the name and the recent change in length.
The term comes from ISO/IEC 7812, the international standard for identification cards that defines how a card number is structured. Under that standard, the first digit is the major industry identifier, the leading digits together form the IIN, the remaining digits identify the individual account, and the last digit is a check digit calculated with the Luhn formula. The standard uses "issuer" rather than "bank" because many issuers are not banks: payment companies, retailers, fuel card providers and the networks themselves can all hold ranges.
For decades the IIN was six digits long. A revision of ISO/IEC 7812 published in 2015 extended it to eight digits, because six-digit ranges were running out as card programmes multiplied. Visa and Mastercard set April 2022 as the date by which issuers, acquirers and processors had to handle eight-digit BINs, which affected routing tables, fraud rules and how the primary account number may be shown when truncated. In everyday use "BIN", "IIN" and "BIN range" are treated as interchangeable, and fintech programmes obtain them through BIN sponsorship from a member of the card network.