A subdomain is a website url, which is under a main, or a root domain name. One example is something.domain.com, in which domain.com is the main domain address, while "something" is the subdomain below it. Each subdomain can have its own website 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 also hosted by a separate service provider. Using a subdomain can be quite handy if you wish to have different web sites that are connected in some way. As an example, you may have an online store under the main domain as well as a forum under a subdomain in order to supply means for your customers to ask questions or share views about your products. The main advantage of using a subdomain as opposed to a subfolder is that the sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.