A subdomain is a web address, that's under a main, or a root domain name. An example is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Every subdomain can have its own website and records i.e. aside from employing the domain name as a part of the whole web address, a subdomain can be fully independent and even hosted by a separate service provider. Employing a subdomain can be very useful if you wish to have different web sites that are associated in some way. For instance, you could have an online store under the main domain along with a forum under a subdomain so as to supply means for your clients to ask questions and / or share thoughts concerning your products. The benefit of employing a subdomain as opposed to a subfolder is that the sites are going to be separated, so you are able to update one of them or perform maintenance not affecting the other.