Located immediately to the left of the dot (" . "), the second-level domain is the "readable" part of the domain name. The second-level domain is entirely defined by the registrant, and often refers to the organization or entity associated with the IP address. For example: In http://www.cnn.com "cnn" (Cable News Network) is a second-level domain.
Second-level domains can be divided into further domain levels. For example: http://www.sportsillustrated.cnn.com. These sub domains sometimes represent different computer servers within departments. More than one second-level domain name can be used for the same IP address.