A subdomain is a website address, that's under a main, or a root domain name. An illustration 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 site and records i.e. apart from employing the domain name as part of the whole web address, a subdomain can be entirely independent and also hosted by a separate company. Employing a subdomain can be extremely useful if you'd like to have different websites which are associated in some way. For example, you can have an on-line store under the main domain along with a forum under a subdomain in order to supply means for your customers to ask questions and share views concerning your products. The advantage of employing a subdomain rather than a subfolder is that the sites will be separated, so you are able to update one of them or perform maintenance not affecting the other.