A subdomain is a web address, that's under a main, or a root domain name. An 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 different company. Employing a subdomain can be very practical if you wish to have different web sites that are related in some way. As an example, you can have an on-line store under the main domain as well as a forum under a subdomain in order to offer means for your clients to ask questions and / or share thoughts about your products. The advantage of using 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.