A subdomain is a web address, that is under a main, or a root domain name. One example is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Each subdomain can have its own website and records i.e. apart from using the domain name as part of the whole web address, a subdomain can be fully independent and also hosted by a different provider. Employing a subdomain can be very useful if you wish to have different web sites that are connected in some way. For example, you may have an online store under the main domain along with a forum under a subdomain so as to provide means for your clients to ask questions and / or share experiences regarding your products. The main advantage of employing a subdomain as opposed to a subfolder is that the sites are going to be separated, so that you can update one of them or perform maintenance without affecting the other.