A subdomain is a website url, that's under a main, or a root domain name. One example is something.domain.com, in which domain.com is the main domain address, while "something" is the subdomain below it. Each and every subdomain can have its own website and records i.e. apart from employing the domain name as a part of the whole web address, a subdomain can be totally independent and also hosted by a separate provider. Using a subdomain could be very practical if you'd like to have different web sites that are associated in some way. For instance, you may have an online store under the main domain along with a forum under a subdomain in order to provide means for your clients to ask questions and share views about your products. The advantage of employing a subdomain instead of 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.