A subdomain is a web address, that is under a main, or a root domain. An illustration is something.domain.com, where domain.com is the main domain name, while "something" is the subdomain below it. Each subdomain can have its own site and records i.e. apart from employing the domain name as part of the whole web address, a subdomain can be completely independent and also hosted by a different service provider. Employing a subdomain can be very handy if you'd like to have different sites that are connected in some way. For instance, you could have a web-based store under the main domain plus a forum under a subdomain in order to offer means for your customers to ask questions and share views about your products. The main advantage of employing a subdomain rather than a subfolder is that the sites will be separated, so you're able to update one of them or perform maintenance without affecting the other.