A subdomain is a website url, that's under a main, or a root domain name. One example is something.domain.com, where 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 totally independent and also hosted by a separate company. Employing a subdomain can be quite practical if you'd like to have different sites that are related in some way. For instance, you could have a web-based store under the main domain and a forum under a subdomain in order to offer means for your customers to ask questions and share views regarding your products. The benefit of employing a subdomain rather than a subfolder is that the web sites will be separated, so that you can update one of them or perform maintenance not affecting the other.