A subdomain is a website url, which is under a main, or a root domain. An illustration is something.domain.com, in which domain.com is the main domain name, while "something" is the subdomain below it. Each 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 service provider. Employing a subdomain can be quite useful if you wish to have different web sites which are associated in some way. As an example, you could have a web-based store under the main domain along with a forum under a subdomain in order to supply means for your clients to ask questions and / or share opinions regarding your products. The main advantage of using a subdomain as opposed to a subfolder is that the web sites are going to be separated, so you're able to update one of them or perform maintenance without affecting the other.