A subdomain is a web address, that is under a main, or a root domain. One example is something.domain.com, in which 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. aside from using the domain name as a part of the whole web address, a subdomain can be entirely independent and even hosted by a separate service provider. Employing a subdomain could be very practical if you'd like to have different sites which are connected in some way. For instance, you could have an on-line store under the main domain and a forum under a subdomain in order to provide means for your customers to ask questions and / or share thoughts regarding your products. The benefit of using a subdomain rather than a subfolder is that the websites will be separated, so you are able to update one of them or perform maintenance not affecting the other.