A subdomain is a website address, which is under a main, or a root domain name. An illustration is something.domain.com, in which domain.com is the main domain, while "something" is the subdomain below it. Each 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 entirely independent and even hosted by a different provider. Employing a subdomain can be very practical if you wish to have different sites which are associated in some way. For example, you may have an on-line store under the main domain as well as a forum under a subdomain so as to offer means for your clients to ask questions and / or share experiences regarding your products. The benefit of using a subdomain rather than a subfolder is that the web sites will be separated, so you can update one of them or perform maintenance without affecting the other.