Independent sales organization (ISO)
A third-party company that sells merchant accounts on behalf of an acquirer, without being a bank or owning the merchant relationship as far as the card networks are concerned.
Card networks only admit banks as members, and acquiring banks rarely want to send salespeople to every pizzeria in town. The answer was a layer of sales companies. An ISO is registered with Visa through a sponsoring acquirer (Mastercard calls the same role a Member Service Provider), signs up merchants, installs the terminal and collects an ongoing cut of the fees, known as residuals. The contract and the risk formally stay with the bank.
The industry's reputation is mixed. In the US, ISO reps became notorious for four-year non-cancellable terminal leases on machines that could be bought outright for a fraction of the total. The difference from a payment facilitator is that an ISO only sells, while a payfac takes in the money itself and carries the liability.