A subdomain is a website url, which is under a main, or a root domain name. One example is something.domain.com, in which domain.com is the main domain name, 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 a part of the whole web address, a subdomain can be entirely independent and also hosted by a different company. Employing a subdomain could be very useful if you want to have different websites that are connected in some way. As an example, you could have an on-line 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 experiences about your products. The main advantage of using a subdomain rather than a subfolder is that the websites will be separated, so you can update one of them or perform maintenance without affecting the other.