A subdomain is a website url, which is under a main, or a root domain name. An illustration is something.domain.com, where 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. apart from employing the domain name as a part of the whole web address, a subdomain can be fully independent and also hosted by a different company. Employing a subdomain can be quite beneficial if you want to have different sites that are related in some way. As an example, you could have an online store under the main domain plus a forum under a subdomain in order to provide means for your customers to ask questions or share views about your products. The advantage of using a subdomain rather than 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.
