A subdomain is a web address, which is 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. Every single subdomain can have its own website and records i.e. apart from using the domain name as a part of the whole web address, a subdomain can be completely independent and also hosted by a separate company. Employing a subdomain could be very useful if you'd like to have different sites that are related in some way. As an example, you can have an online store under the main domain and a forum under a subdomain so as to supply means for your customers to ask questions or share opinions about your products. The best thing about employing 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 not affecting the other.