A subdomain is a website url, which is under a main, or a root domain. 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 using the domain name as part of the whole web address, a subdomain can be fully independent and even hosted by a different company. Employing a subdomain can be quite practical if you wish to have different websites which are connected in some way. For example, you can have a web-based store under the main domain along with a forum under a subdomain so as to supply means for your customers to ask questions and / or share experiences concerning your products. The best thing about employing a subdomain rather than 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.