Hello,
E-commerce means Electronic Commerce.
Electronic Commerce or e-commerce is the activity of buying or selling of products over the internet.
There are mainly six types of e-commerce

1. Business-to-Business (B2B),
2. Business-to-Consumer (B2C),
3. Consumer-to-Consumer (C2C),
4. Consumer-to-Business (C2B)
5. Business-to-Administration (B2A) and
6. Consumer-to-Administration (C2A)

Here are few examples of e-commerce websites-
Amazon, Flipkart,OLX ,Myntra,Quikr.

Hope it helps :)