A payment gateway is a service that connects your online store with your merchant account provider. This service reads the information from the order forms and translates that information for the merchant account. The payment gateway also verifies that the customer's credit card account has the necessary credit available for the purchase.
A party which provides an interface between Merchant POS systems, Acquirer payment systems, and Issuer payment systems.
a service that provides connectivity among merchants, customers and financial networks to process and authorize payments