A subdomain is a web address, which is under a main, or a root domain. An illustration is something.domain.com, in which domain.com is the main domain address, while "something" is the subdomain below it. Every single subdomain can have its own website and records i.e. aside from employing the domain name as a part of the whole web address, a subdomain can be completely independent and even hosted by a different service provider. Employing a subdomain can be quite practical if you want to have different websites which are related in some way. As an example, you can have an on-line store under the main domain along with a forum under a subdomain in order to provide means for your clients to ask questions or share experiences about your products. The advantage of employing a subdomain as opposed to a subfolder is that the websites will be separated, so you are able to update one of them or perform maintenance not affecting the other.