A subdomain is a website url, that's under a main, or a root domain name. One example 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 a part of the whole web address, a subdomain can be fully independent and also hosted by a separate company. Employing a subdomain could be very beneficial if you wish to have different sites that are associated in some way. For example, you may have a web-based store under the main domain and a forum under a subdomain in order to supply means for your clients to ask questions and / or share views about your products. The best thing about employing a subdomain as opposed to a subfolder is that the web sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.