A subdomain is a website url, that's under a main, or a root domain. An example is something.domain.com, in which domain.com is the main domain name, while "something" is the subdomain below it. 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 totally independent and also hosted by a separate provider. Employing a subdomain could be very useful if you want to have different web sites that are related in some way. As an example, you can have a web-based store under the main domain as well as a forum under a subdomain so as to provide means for your customers to ask questions and / or share opinions concerning your products. The main advantage of employing a subdomain instead of a subfolder is that the web sites are going to be separated, so you're able to update one of them or perform maintenance without affecting the other.