What Are Sub Domains
Sub domains can be more simply described as the domains which fall under the category of the main Domain Name System or the DNS. The most general example of this would be that example.com is the sub domain of the com which is known to be the TLD or the top level domain while www.example.com is a service in the domain example.com.
It can also be stated that the top level domain "com" is actually the sub domain of the root domain which is "." This series is similar to the easier concept of the drive, folder and file relationship. In the DNS or the Domain Name System the names are originally written in the descending hierarchy of right to left.
The sub domain is a part of a larger domain which is the called its parent domain or also sometimes known as the super domain. The term parent domain is more commonly used and preferred over super domain.
The word sub domain shows the relative dependence of the domain for example the domain wikipedia.org contains a sub domain which is from the org domain, whereas the domain en.wikipedia.org contains the sub domain which is of the domain wikipedia.org itself. This subdivision is known to go down to 127 further levels deep, which can exceed, however no domain name goes beyond the limit of 255 characters.
The sub domain is also given the name of "vanity domain" most commonly; this is most common in a situation when the sub domain is of the ISP's own domain linked to an individual account.
Sub domains are helpful for those companies who wish to opt for a unique name to a specific department or function in the organization. For example the various different departments of a university can be assigned with its corresponding domain, like the sciences department can have the sub domain of 'sci' in the domain.