Understanding Domain Structure for Beginners

Author: John Ward

Many people often confuse with the terms domain, top level domain (TLD), root domain, sub domain and sub directory/sub-folder. Some people use them interchangeably whereas in reality, each of them is distinct.

First, domain or domain name is the user readable form of address or URL (Uniform Resource Locator) that user types in the address bar of the browser to visit the website. Some examples of domains are:

  • www.example1.com
  • Blog.rootdomain.net
  • City.website.us/subfolder

The domain or URL contains different parts like top level domain, root domain, sub-domain and sub-folder. Let’s discuss them briefly.

Top level domain (TLDs)

A top level domain appears at the end of the URL followed by a period. In the above examples, ‘com’, ‘net’ and ‘us’ are the top level domains.

TLDs can be standard ones such as ‘com’ for commercial websites, ‘org’ for organizations, ‘net’ for networks, etc. They can be a country code like ‘us’ for USA, ‘ca’ for Canada, etc.

Root domain

Any domain will have only one root domain and has to be purchased or registered from registrars.

It is the second level domain in hierarchy and is the primary portion of a website. Root domains are also called secondary domains. In our above examples, ‘example1’, ‘rootdomain’ and ‘website’ are the root domains.

TLDs and root domains are very essential and they are required to be entered in browser or other software or applications to find the website.

Sub-domain

A sub-domain is part of the root domain and it is called third level domain. A root domain can have any number of sub domains. They are free of cost but need to be set up. For example, ‘www’, ‘Blog’ and ‘City’ are subdomains of the root domains ‘example1’, ‘rootdomain’ and ‘website’.

Sub-domains are treated as separate websites. They do not carry the credibility or quality metrics of the root domain. They have to build their own. The credibility of the root domain is not passed to it unless it is linked.

A sub-domain is useful if the website

  • Has multiple geographic pages
  • Offers different products/services
  • Appears in different languages

A sub-domain is helpful as buying a new domain involves additional cost to the business.

Sub-directory

A sub-directory is also called a folder and is used instead of sub-domain. It's part of the root domain or sub-domain on which it is created. It's treated as a folder in the domain (could be root domain or sub-domain).

For example, in City.website.us/subdirectory, ‘subdirectory’ is the folder created

A sub-directory is useful

  • When you want to boost content and authority of your main website
  • When you do not have budget to do SEO for more than one website (sub-domains are considered as different website and need separate SEO, separate content and marketing strategy)