A subdomain is a website address, that is under a main, or a root domain name. An example is something.domain.com, where domain.com is the main domain name, while "something" is the subdomain below it. Each 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 different company. Employing a subdomain can be extremely beneficial if you'd like to have different web sites that are connected in some way. As an example, you may have a web-based store under the main domain and a forum under a subdomain so as to provide means for your clients to ask questions and / or share views regarding your products. The best thing about employing a subdomain rather than a subfolder is that the web sites will be separated, so you're able to update one of them or perform maintenance without affecting the other.