What is a Domain Name?
A unique name that identifies an Internet site. Domain names always have at least two parts, separated by dots. For example, the domain name for this site is Sutherdyne.com. Note that the "www" is not part of the actual domain name. The "www" only says that this address is on the "World Wide Web" (as opposed to a mail address, FTP address, etc).
The "Top Level Domain" is the part on the right of the domain name. .com, .org, .net, .gov are some of the more common top level domains. The "Sub-Domain" is the part you get to pick, for example "Sutherdyne". Together, the Sub-Domain and the Top Level Domain make up the Domain Name.