Subdomains are a way of creating separate domain within your master domain, which are accessed as separate URLs.
For example, you could set up a "yourname" subdomain on your master account "maindomain.com", which would be accessed as "yourname.maindomain.com". However, you do not create a new cPanel when you create a subdomain. You still perform most administration functions for the subdomain through your master cPanel.
Practically, a subdomain is a sub folder within the public_http level of your account that has it's own cgi-bin directory.
