A subdomain is a website url, which is under a main, or a root domain name. An illustration is something.domain.com, in which 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 a part of the whole web address, a subdomain can be totally independent and even hosted by a different service provider. Employing a subdomain can be quite beneficial if you wish to have different sites that are related in some way. As an example, you may have an on-line store under the main domain along with a forum under a subdomain so as to offer means for your customers to ask questions and / or share views regarding your products. The advantage of using a subdomain rather than a subfolder is that the sites are going to be separated, so you're able to update one of them or perform maintenance not affecting the other.