An issuing bank is the bank that provides a payment card to a customer, runs the credit line or deposit account behind it, and decides in real time whether to approve each transaction. It is also called the issuer or cardholder's bank. Because the role can also be filled by credit unions and licensed non-banks, Money Wiki covers it in full under Card Issuer.
In the four-party model used by Visa and Mastercard, the issuing bank sits opposite the acquiring bank, which serves the merchant, with the card scheme in between. On most card sales the issuer receives interchange, a fee paid by the acquirer, which helps fund rewards and cover fraud losses. Many fintech card programmes are not issuers themselves: a licensed bank acts as their BIN sponsor and remains the issuer of record.