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cPanel allows you to create and manage subdomains for your Web Hosting Account.
A subdomain is a "subsection" of your website that can exist as a subdirectory of your /public_html/ (document root) directory or your home directory.
Subdomains use a prefix in conjunction with the domain name.
If the registered domain name is php-fusion.co.uk, with the desired subdomain of "domain" would look like: domain.php-fusion.co.uk
This type of Domain or subdomain works just as a separate Domain.
Even the Search Engines treat these as completely different domain names.
You can also use subdomains to create unique user account or for a specific subject.
This is useful if you have a blog, or any other type of website that uses a domain specifically titled for a user or subject.