Merchant Accounts & Payment Gateways
Electronic Commerce, or E-Commerce, is the buying and selling of goods and services, using electronic means. In other words, doing business using computerized devices on the internet. In terms of software solutions for business, it generally refers to selling items online using an e-commerce store.
That storefront (think catalog) is then linked to a shopping cart that offers various payment methods (Payment Gateways to process credit cards) to the customers and processes those payments using a merchant service (handling the money until it goes into your account). So, to do business online, you need both a payment gateway and a merchant account. Some providers offer both.
This can be confusing. Here is a great article describing the difference: Payment Gateways vs Merchant Accounts.
PayPal - aggregate merchant account and payment gateway
Stripe - aggregate merchant account and payment gateway
QuickBooks Merchant Services - dedicated merchant account
Authorize.net - dedicated merchant account and payment gateway