A subdomain is a web address, that's under a main, or a root domain name. An illustration 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 employing the domain name as part of the whole web address, a subdomain can be fully independent and also hosted by a different company. Using a subdomain can be very useful if you want to have different web sites which are connected in some way. As an example, you can have a web-based store under the main domain plus a forum under a subdomain so as to offer means for your clients to ask questions and share views regarding your products. The main advantage of employing a subdomain instead of a subfolder is that the web sites are going to be separated, so you're able to update one of them or perform maintenance not affecting the other.