A subdomain is a website url, which is under a main, or a root domain name. One example is something.domain.com, where domain.com is the main domain name, while "something" is the subdomain below it. Each and every subdomain can have its own website and records i.e. aside from using the domain name as part of the whole web address, a subdomain can be completely independent and even hosted by a separate service provider. Employing a subdomain can be extremely useful if you wish to have different web sites that are related in some way. For example, you may have an online store under the main domain and a forum under a subdomain so as to supply means for your customers to ask questions or share thoughts about your products. The best thing about employing a subdomain as opposed to a subfolder is that the web sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.