A subdomain is a web address, that's under a main, or a root domain name. An illustration is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Each and every subdomain can have its own website and records i.e. apart from employing the domain name as a part of the whole web address, a subdomain can be entirely independent and also hosted by a separate company. Employing a subdomain can be extremely useful if you wish to have different sites that are associated in some way. For example, you may have a web-based store under the main domain plus a forum under a subdomain so as to provide means for your customers to ask questions or share opinions regarding your products. The benefit of using a subdomain as opposed to a subfolder is that the websites are going to be separated, so that you can update one of them or perform maintenance not affecting the other.