A subdomain is a website address, that's under a main, or a root domain name. One example is something.domain.com, where domain.com is the main domain, while "something" is the subdomain below it. Every subdomain can have its own site and records i.e. apart from using the domain name as a part of the whole web address, a subdomain can be completely independent and also hosted by a separate service provider. Using a subdomain can be quite useful if you wish to have different websites which are connected in some way. For instance, you could have an on-line store under the main domain and a forum under a subdomain in order to supply means for your clients to ask questions and share opinions about your products. The advantage of employing a subdomain instead of a subfolder is that the web sites will be separated, so you're able to update one of them or perform maintenance not affecting the other.