A subdomain is a website url, which is under a main, or a root domain. One example is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Each and every subdomain can have its own site and records i.e. apart from using the domain name as a part of the whole web address, a subdomain can be totally independent and also hosted by a different company. Using a subdomain can be very handy if you want to have different web sites that are connected in some way. For instance, you could have an on-line store under the main domain along with a forum under a subdomain so as to provide means for your clients to ask questions or share opinions concerning your products. The main advantage of employing a subdomain rather than a subfolder is that the web sites will be separated, so you're able to update one of them or perform maintenance not affecting the other.