A subdomain is a web address, that's under a main, or a root domain. One example 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 using the domain name as a part of the whole web address, a subdomain can be fully independent and also hosted by a different company. Using a subdomain can be quite beneficial if you'd like to have different sites which are associated in some way. For instance, you may have an on-line store under the main domain and a forum under a subdomain in order to offer means for your clients to ask questions and / or share views concerning your products. The advantage of employing a subdomain as opposed to a subfolder is that the websites are going to be separated, so you're able to update one of them or perform maintenance not affecting the other.