Online business - also referred to as e-business - is any kind of business activity that happens online (over the internet).
A business owner who does any, or all, of their business using the internet, is running an online business. Running an online business can include buying and selling online, and providing an online service. A wide variety of businesses can be found online, in many different industries.
Anyone can start an online business. If you have a unique product or idea, you can find a way to sell or trade it online. It's just like a traditional 'bricks-and-mortar' business, except your office or shop is online, so you have to decide how it will look and appeal to customers.