A subdomain is a web address, which is under a main, or a root domain name. An example is something.domain.com, in which domain.com is the main domain name, 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 completely independent and also hosted by a separate provider. Using a subdomain can be extremely beneficial if you want to have different web sites that are related in some way. As an example, you may have a web-based store under the main domain and a forum under a subdomain so as to provide means for your customers to ask questions or share opinions about your products. The best thing about using a subdomain as opposed to a subfolder is that the websites will be separated, so you're able to update one of them or perform maintenance without affecting the other.