Domain Name has various meanings. It could be the name entered by the users in their address bar of the computer and then looked up in the global Domain Name System-DNS to visit the particular site. All domain names have their own assigned IP address and the DNS translates the IP address into words. It could also be a unique address on the Internet referred to as Internet address. Domain names are also referred to as Uniform Resource Locaters or URLs.

In DNS a label could be the digits, hyphens and each string of letters used between the dots. There are certain rules that are applied for these valid labels which have been changed with time. Before labels had to begin with a letter and end with a letter or digit .Any intervening characters may be letters, digits, or hyphens. They must be between 1 and 63 characters long. Now they can begin with a digit and can have internal underscores but no domain name can be all numeric. These rules depend on the domain level. Some top level domains have more rules.

URL and Domain name:
The difference between a URL and a domain name:
URL: http://www.xyz.com/
Domain name: xyz.com

A domain name can have more than one IP address and more than one domain name assigned to an IP address. At the same time one server can have multiple roles, and one role can be applied for multiple servers. One IP address can even be assigned to several servers. The IP address and the server name are interchangeable. This makes it impossible for the server to know which IP address was used. But with the help of HTTP- hypertext transfer protocol, you need to specifically tell the server which domain name is being used. So, one server with one IP address can provide different sites for different domain names.

Say, the server particular server covers all these sites:
xyz.com
xyz.net
xyz.org

When you put a request, then you will get the data corresponding to the host name requested.

Domain Levels:
Top-level domain

The end of all domain names is called top level domain. Say, xyz.edu or xyz.net or xyz.org etc where edu, net and org are all top level domain. This could be a list of generic names or a 2 character territory code like .ac or .ad or .in which are country code top level domains.

Second level domain

Second-level domain names are directly to the left of .com.net, and the other top-level domains. For example: en.xyz.net where xyz is the second level domain.

Third level domain

The next level i.e. the third-level domains are to the left of a second-level domain. Here en is the third level domain.