A subdomain is a website url, which is under a main, or a root domain. One example 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 fully independent and also hosted by a separate provider. Using a subdomain can be quite handy if you'd like to have different sites that are associated in some way. For instance, you can have an on-line store under the main domain plus a forum under a subdomain in order to offer means for your customers to ask questions and share experiences concerning your products. The advantage of employing a subdomain as opposed to a subfolder is that the websites will be separated, so you can update one of them or perform maintenance not affecting the other.