What are commercial websites? Commercial websites are any site that ends with the domain extension '.com'. Domain extensions are more accurately called Top Level Domains or TLDs. The '.com' TLD represents the word "commercial," and is the most widely used extension in the world. Most businesses prefer a .com domain name because it is a highly recognized symbol for having a business presence on the Internet.
A lot of website owners use domain name extensions improperly. For example, if someone creates a personal blog and there's no commercial activity, it shouldn't have the '.com' TLD, yet there are many personal '.com' websites. Basically, a '.com' website should be any site that Buys, Sells, or provides a service for a fee.
'.co' stands for Country code top-level domain or cccTLD representing the district of Columbia. Some companies are using the '.co' and inferring that is stands for '.com' only shorter, but this is really improper use of '.co'. Because major companies like Google (http://g.co/) and Aspen (http://www.aspen.co/) have started misusing the '.co' domain extension to represent '.com' and since, it has become widely accepted that '.co' can represent commercial websites.