Several terms like payment gateway, payment processor, payment provider, payment service or system, and merchant accounts can be used when describing online payments. All of them refer to a company, service or application that acts as a middleman between your website and your customer and then between both your bank accounts. They enable the completion of online transactions and the processing of online payments.
As you have read above, all the terms that online payment services can be referred as, have some subtle changes in them, which is always good for us to be aware of.