A Bank Identification Number (BIN) is the first six digits of a credit card, debit card, charge card, etc. These digits identify which network the card belongs to as well as which bank issued it.
Online merchants may use BIN lookups to help validate transactions. For example, if the credit card's BIN indicates a bank in one country, while the customer's billing address is in another, the transaction may call for extra scrutiny.
The term "Issuer Identification Number" (IIN) is replacing "Bank Identification Number".