Payment Processor
The company that moves a transaction between the customer’s bank, the card networks, and the merchant’s acquirer.
A payment processor is the company that routes a transaction between your gateway, the card networks and the banks, and moves the resulting funds. It is the operational engine behind the account rather than the underwriter of it.
In a typical arrangement several parties are involved: the gateway captures the payment, the processor routes it, and an acquiring bank sponsors the merchant account and holds the risk. Some businesses combine these roles, which is convenient but means one commercial relationship controls every layer at once.
For high-risk merchants the question worth asking is which sponsor banks a processor can place business with. A processor with a single banking relationship can only offer what that bank accepts, so a change in that bank's appetite becomes your problem immediately and with little notice.
Processing on more than one processor is what turns a closure from an outage into an inconvenience, because transactions can move to another rail while the first is resolved.