A subdomain is a website address, that's under a main, or a root domain. An example is something.domain.com, where domain.com is the main domain name, while "something" is the subdomain below it. Each and every subdomain can have its own site and records i.e. aside from employing the domain name as a part of the whole web address, a subdomain can be entirely independent and also hosted by a different company. Employing a subdomain could be very handy if you wish to have different sites that are connected in some way. For instance, you can have an on-line store under the main domain and a forum under a subdomain so as to offer means for your clients to ask questions and / or share views concerning your products. The benefit of using a subdomain rather than a subfolder is that the sites will be separated, so that you can update one of them or perform maintenance without affecting the other.