A subdomain is a website address, that's 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. Each and every subdomain can have its own site and records i.e. aside from employing the domain name as part of the whole web address, a subdomain can be entirely independent and even hosted by a different company. Using a subdomain can be extremely beneficial if you wish to have different websites which are associated in some way. For instance, you could have an on-line store under the main domain plus a forum under a subdomain in order to supply means for your clients to ask questions and share experiences concerning your products. The best thing about employing a subdomain as opposed to a subfolder is that the websites will be separated, so that you can update one of them or perform maintenance not affecting the other.