Ecommerce - Electronic Commerce Online Business
e-Commerce: Refers to the business done by taking help of the Internet. It is also knows as Online Business. 
B2B(Business to Business): The B2B used between businessman is order to have transaction or sale-purchase of goods.
Payment Gateway: A gateway to process online transactions in e-commerce.

Check Out :
1. What is e-Commerce?
2. Payment Gateways
3. e-Commerce in India
4. How to start an e-business?