A subdomain is a website url, which is under a main, or a root domain name. An example is something.domain.com, where 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 could be very handy if you wish to have different sites that are related in some way. For example, you can have an on-line store under the main domain and a forum under a subdomain so as to supply means for your clients to ask questions and / or share views regarding your products. The main advantage of employing a subdomain instead of a subfolder is that the sites will be separated, so you can update one of them or perform maintenance without affecting the other.