A subdomain is a part of a web address that's under the main domain, for instance name.example.com. Actually, even in www.example.com the "www" element is a subdomain given that the fully qualified domain name is only "example.com". Every subdomain can have its own web site and records and can also be hosted with a different company if you wish to use a specific feature which is not provided by your current provider. An example for using a subdomain is if you have a company site as well as an online store under a subdomain where customers can acquire your products. You can also have a forum in which they can talk about the products and by employing subdomains as opposed to subfolders you are going to avoid any risk of all sites going down if you perform maintenance, or update one of the website scripts. Keeping your sites separated is more secure in the event of a script security breach.
