A subdomain is a web address, that is under a main, or a root domain. An illustration is something.domain.com, in which domain.com is the main domain, while "something" is the subdomain below it. Each and every subdomain can have its own website and records i.e. apart from using the domain name as part of the whole web address, a subdomain can be entirely independent and also hosted by a separate company. Employing a subdomain could be very beneficial if you'd like to have different sites which are connected in some way. For instance, you could have a web-based store under the main domain along with a forum under a subdomain so as to supply means for your clients to ask questions or share thoughts concerning your products. The advantage of employing a subdomain instead of a subfolder is that the sites are going to be separated, so that you can update one of them or perform maintenance not affecting the other.