A subdomain is a website url, that's 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 and every subdomain can have its own website and records i.e. apart from employing the domain name as part of the whole web address, a subdomain can be totally independent and even hosted by a different company. Using a subdomain can be quite beneficial if you wish to have different websites that are associated in some way. For example, you could have a web-based store under the main domain as well as a forum under a subdomain so as to supply means for your clients to ask questions and / or share experiences concerning your products. The advantage of employing a subdomain as opposed to a subfolder is that the websites will be separated, so you're able to update one of them or perform maintenance not affecting the other.