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. Each 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 provider. Employing a subdomain could be very handy if you'd like to have different websites which are associated in some way. For instance, you can have a web-based store under the main domain and a forum under a subdomain so as to supply means for your customers to ask questions and / or share views concerning your products. The main advantage of using a subdomain instead of a subfolder is that the sites are going to be separated, so you're able to update one of them or perform maintenance without affecting the other.