Put simply, eCommerce is the interaction between businesses and consumers through the buying and selling of goods or services. Most eCommerce is B2C however B2B is used as well for wholesaling and drop shipping.
eCommerce is where an electronic transfer of funds takes between a consumer and a website, in exchange for goods or services. It is available 24/7 and from a global platform via the internet.
However, sites like eBay and Etsy have enabled C2C to take place. This is where consumers make a product or post a used item for other consumers to bid on and purchase. C2B can also now take place as consumers are able to outsource work from a company overseas by posting the project online and having companies offer a price to complete it.