Any person, organization or company that accepts credit or debit card payments that are properly presented is a merchant. This can include a retailer, an online seller, a charity or any other kind of organization that hold a merchant account and participates in a merchant agreement.
UniPay Gateway: Open Source Payment Gateway
How to Choose the Best Payment Solution
How to Own a Payment Gateway
What is a Payment Gateway
What is Recurring Billing?
How Payments Work
What Should an Ideal Payment Platform for Investors Look Like?