Sub Domains (also known as "third-level-domains")
A Sub Domain is a domain which is part of its parent domain or primary domain.
For example: is a parent domain whereas is a sub domain (still part of the main domain).
Why use Sub Domains
Sub domains have their uses when a company wishes to split their website into main sections or product areas. Indeed there are advantages to this:
  • There is no additional cost (or shouldn’t be!) for adding a sub domain.
  • When a site is very large it makes sense to create individual sectors for large areas, enabling better management of site content.
  • Sub domains can be used very efficiently for brand awareness and focussing.
  • The sub domain will be recognised in it’s own entity by users and search engines allowing webmasters and SEO companies to concentrate on sub domains individually (apart from the main domain).
  • What Not to do with Sub Domains
    There is much controversy on the web about sub domains, mainly in relation to search engines and what they will or will not accept.

    One basic issue to avoid when using a sub domain is:
    Don’t use sub domains to publish duplicate (or near duplicate) content hoping that you will increase your chances of being found by search engines. A search engine could well deem this as a ‘spamming’ technique and de-list you from its index entirely.