What Is a Subdomain?

Subdomains help you organise large, complex websites.

A subdomain is an element (or ‘label’) that can be used in a URL to separate parts of a large or complex website into standalone resources. For example, it could describe a department of a large company.

It’s also known as a ‘low-level domain’ or ‘child domain’, alongside the top-level domain (.com, .co.uk, or .info, for example), and the mid-level domain, which is usually the name of the main website.

The subdomain, mid-level domain and top-level domain are separated by dots.

So, in the URL https://business.yell.com:

  • marketing is the subdomain
  • yell is the second-level domain
  • .com is the top level domain

Subdomains vs subfolders

You can use subdomains, subfolders or a combination of both to organise your site.

For example, look at the URL for this page –

  • marketing.yell.com is divided as explained above
  • web-design is a subfolder, with advice and articles on web design
  • what-is-a-subdomain is the article you’re reading

What are subdomains used for?

Subdomains can be helpful in organising very large and complex sites, especially ones that have several large, discrete sections.

It will often be cheaper and easier to maintain several subdomains that to have several separate websites – as some hosting companies will not charge extra for additional subdomains.

You’ll also only have to remember one set of payment, expiration and login details for maintenance.

Subdomains could also help you boost your search engine optimisation, by allowing you to get targeted keywords into your domain name.

However, this will only boost SEO results for the subdomain, and not for the main site – as most search engines treat subdomains as separate sites.