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, while "something" is the subdomain below it. Each and every subdomain can have its own site and records i.e. aside from employing the domain name as part of the whole web address, a subdomain can be fully independent and even hosted by a different service provider. Employing a subdomain can be very practical if you want to have different sites which are related in some way. As an example, you may have a web-based store under the main domain and a forum under a subdomain in order to provide means for your clients to ask questions or share thoughts concerning your products. The best thing about using a subdomain as opposed to a subfolder is that the websites will be separated, so you're able to update one of them or perform maintenance not affecting the other.