Acquirer
The bank or payments company that accepts card payments on a merchant's behalf and makes sure the money lands in the merchant's account.
Card payments follow the so-called four-party model. The cardholder deals with their issuer, the merchant deals with their acquirer, and a card network such as Visa or Mastercard sits between the two. When a card is used, the acquirer sends an authorisation request through the network to the issuer, which says yes or no within a second or so. The money itself moves later, during clearing and settlement.
The acquirer underwrites the merchant. If a shop goes bust with hundreds of unfulfilled pre-orders, the acquirer is left holding the customers' chargebacks. That is why acquirers vet merchants carefully and sometimes demand collateral. The job used to belong to the big banks, but today it is dominated by firms such as Adyen and Worldpay.