A subdomain is a web address, that is under a main, or a root domain name. An illustration is something.domain.com, in which domain.com is the main domain address, while "something" is the subdomain below it. Each and every subdomain can have its own site and records i.e. aside from using the domain name as a part of the whole web address, a subdomain can be totally independent and even hosted by a different service provider. Using a subdomain can be quite practical if you wish to have different web sites that are related in some way. For example, you could have an on-line store under the main domain as well as a forum under a subdomain so as to provide means for your clients to ask questions and share experiences regarding your products. The benefit of employing a subdomain as opposed to a subfolder is that the web sites will be separated, so you can update one of them or perform maintenance without affecting the other.