A subdomain is a website url, 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. Every subdomain can have its own website and records i.e. aside from using the domain name as part of the whole web address, a subdomain can be fully independent and even hosted by a separate company. Using a subdomain can be quite practical if you want to have different web sites which are related in some way. As an example, you can have a web-based store under the main domain as well as a forum under a subdomain so as to supply means for your clients to ask questions and share views about your products. The main advantage of employing a subdomain rather than a subfolder is that the sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.