A subdomain is a website url, that is under a main, or a root domain name. One example is something.domain.com, where domain.com is the main domain address, while "something" is the subdomain below it. Every single subdomain can have its own site and records i.e. aside from employing the domain name as part of the whole web address, a subdomain can be fully independent and also hosted by a different company. Using a subdomain could be very handy if you wish to have different websites that are associated in some way. For example, you may have an online store under the main domain as well as a forum under a subdomain in order to offer means for your clients to ask questions and / or share opinions about your products. The main advantage of employing a subdomain instead of a subfolder is that the web sites will be separated, so you can update one of them or perform maintenance not affecting the other.