A subdomain is a domain that is part of a larger domain name. Basically a subdomain is a third level domain that is used to organize your Web site content, but it appears before your domain name. Subdomains are just like folders under your root directory, but they will have a special URL to access.
is the regular URL with out a subdomain, but
is a URL with the subdomain “products”.
The Domain Name System (DNS) has a tree structure or hierarchy, with each node on the tree being a domain name. For more information, see domain name.
NetLingo Classification: Net Programming