A subdomain is a website url, that's under a main, or a root domain name. An illustration is something.domain.com, where domain.com is the main domain, while "something" is the subdomain below it. Each subdomain can have its own site and records i.e. apart from using the domain name as a part of the whole web address, a subdomain can be totally independent and even hosted by a different service provider. Employing a subdomain can be extremely practical if you'd like to have different web sites which are associated in some way. As an example, you may have a web-based store under the main domain plus a forum under a subdomain so as to offer means for your clients to ask questions and / or share opinions concerning your products. The best thing about employing a subdomain as opposed to a subfolder is that the web sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.