A subdomain is a website address, which is under a main, or a root domain name. One example is something.domain.com, in which domain.com is the main domain, while "something" is the subdomain below it. 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 completely independent and even hosted by a different company. Using a subdomain can be extremely useful if you wish to have different web sites which are associated in some way. For instance, you may have a web-based store under the main domain plus a forum under a subdomain so as to supply means for your clients to ask questions or share thoughts concerning your products. The advantage of employing a subdomain rather than a subfolder is that the sites will be separated, so that you can update one of them or perform maintenance without affecting the other.