A subdomain is a web address, that is under a main, or a root domain. An example 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 part of the whole web address, a subdomain can be fully independent and even hosted by a different company. Employing a subdomain can be very practical if you want to have different sites that are associated in some way. For example, you may have an on-line store under the main domain along with a forum under a subdomain so as to provide means for your clients to ask questions and / or share experiences regarding your products. The best thing about employing a subdomain as opposed to a subfolder is that the websites are going to be separated, so you can update one of them or perform maintenance without affecting the other.