A subdomain is a website url, that's 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. Every subdomain can have its own website and records i.e. apart from using the domain name as a part of the whole web address, a subdomain can be entirely independent and also hosted by a separate provider. Using a subdomain can be quite handy if you'd like to have different sites which are related in some way. For instance, you could have an online store under the main domain as well as a forum under a subdomain in order to supply means for your customers to ask questions or share views regarding your products. The benefit of employing a subdomain as opposed to a subfolder is that the web sites will be separated, so you can update one of them or perform maintenance without affecting the other.