A subdomain is a website url, which is under a main, or a root domain. An example is something.domain.com, in which 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 a part of the whole web address, a subdomain can be totally independent and even hosted by a separate provider. Employing a subdomain can be quite beneficial if you wish to have different web sites which are associated in some way. For instance, you may have an on-line store under the main domain plus a forum under a subdomain so as to provide means for your clients to ask questions or share views concerning your products. The advantage of employing a subdomain as opposed to a subfolder is that the websites are going to be separated, so that you can update one of them or perform maintenance without affecting the other.