Transparency
-"The Name of The Game".
The terms, Payment Processor, Merchant Service Provider: Independent Sale Organization (ISO), Member Service Provider (MSP) or a Payment Service Provider (PSP) have been used interchangeably, creating a confusion on "Who-Is-Who".
A Payment Processor, actually runs the transaction on the back-end, while the others are third party companies that provide the tools and support for a business to accept payments.
A Payment Processor would be; Adyen, Bank of America, Chase Paymentech, Fiserv, just to name a few. While a Independent Sale Organization (ISO) - registered with VISA, Member Service Provider (MSP) - registered with Master Card and a Payment Service Provider (PSP) - unregistered are third party components for accepting payments.
Please Note: Payment Processors, ISO or MSP provide individual merchant accounts with "Merchant Identification Numbers" (MIDs). While a PSP does not provide individual merchant accounts and all payments are pooled into one account.
The information provided is by "NO MEANS" stating or implying anything negative towards anyone or company. It's just to clarify, "Who-Is-Who"!