What is a [domain name]?
Each web site on the internet has a numeric address that functions like coordinates on a map. Instead of pointing to a geographic location on earth, these numeric addresses, called IP addresses, point to a geographical location on the Internet.
The standard domain name consists of three parts:
Second level domain
Root (the "dot")
Top level Domain
Arranged as follows:
second level domain, root, top level domain
So, if your second level domain is second level and you choose the "com" for it, then, when you add the "root," your domain name is second-level.com
So, in short, a domain name is nothing more than a three-part alias for a numeric web address. It's really that simple. If you like to get a more technical explanation, read on!
Domain names are organized according to specific hierarchy, called the DNS naming hierarchy. The DNS naming hierarchy is a tree-like arrangement with ascending authority. Each domain represents a distinct chunk of the naming hierarchy and is managed by a single administrative entity. The root of this "tree" is called "." (the dot in DNS jargon) and beneath it are the top-level (or "root-level") domains. The top-level domains are relatively fixed.
Thus, anyone can register a .com, .net or .org domain. In fact, many companies now register all three domains in order to truly secure their web identity.