A subdomain is a website url, which is 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 using the domain name as a part of the whole web address, a subdomain can be totally independent and even hosted by a different provider. Using a subdomain can be extremely beneficial if you want to have different sites which are connected in some way. As an example, you can have a web-based store under the main domain along with a forum under a subdomain so as to offer means for your customers to ask questions or share opinions regarding your products. The main advantage of employing a subdomain as opposed to a subfolder is that the web sites are going to be separated, so you are able to update one of them or perform maintenance without affecting the other.