A subdomain is a website address, which is under a main, or a root domain. An example is something.domain.com, where domain.com is the main domain, while "something" is the subdomain below it. Each and every subdomain can have its own site and records i.e. apart from using the domain name as part of the whole web address, a subdomain can be totally independent and also hosted by a separate provider. Employing a subdomain can be extremely useful if you wish to have different web sites that are related in some way. For instance, you may have an on-line store under the main domain along with a forum under a subdomain in order to offer means for your clients to ask questions or share opinions about your products. The best thing about using a subdomain instead of a subfolder is that the sites will be separated, so you are able to update one of them or perform maintenance not affecting the other.