A subdomain is a website url, which is under a main, or a root domain name. An example is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Every single 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 completely independent and even hosted by a separate company. Using a subdomain can be extremely handy if you'd like to have different sites that are connected in some way. As an example, you may have an online store under the main domain and a forum under a subdomain in order to provide means for your clients to ask questions and / or share opinions concerning your products. The benefit of employing a subdomain as opposed to a subfolder is that the sites will be separated, so you are able to update one of them or perform maintenance without affecting the other.