E-Commerce can mean a lot of different things to different clients. They are similar in that it is a way for a clients products to be sold on-line, but this can be achieved in different ways.
For some, e-commerce is a simple as an order form with a list of products. The customer enters their information, selects quantities of products they wish to buy, enters payment information which is all processed on a secure server, and this information is sent to the vendor.
For others, a full-featured shopping cart is needed. This cart is set up to contain all the products available, along with prices, weight, images and more. This shopping cart is then used by the customer to purchase these products on-line.