A subdomain is a web address, that's under a main, or a root domain. One 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 website and records i.e. aside from using the domain name as a part of the whole web address, a subdomain can be fully independent and even hosted by a separate company. Employing a subdomain can be extremely beneficial if you want to have different web sites that are connected in some way. As an example, you can have an on-line store under the main domain along with a forum under a subdomain in order to supply means for your clients to ask questions and / or share thoughts concerning your products. The best thing about using a subdomain instead of a subfolder is that the sites are going to be separated, so you can update one of them or perform maintenance without affecting the other.