A subdomain is a website address, which is under a main, or a root domain. An illustration is something.domain.com, where domain.com is the main domain name, while "something" is the subdomain below it. Every single subdomain can have its own site and records i.e. aside from using the domain name as a part of the whole web address, a subdomain can be totally independent and also hosted by a separate service provider. Employing a subdomain can be quite useful if you want to have different sites that are associated in some way. As an example, you can have an on-line store under the main domain and a forum under a subdomain so as to provide means for your customers to ask questions and / or share opinions concerning your products. The advantage of using a subdomain rather than a subfolder is that the websites are going to be separated, so you are able to update one of them or perform maintenance without affecting the other.