A subdomain is the part of the web address that's before a domain name and you have almost certainly seen a lot of subdomains while browsing world wide web. For instance, many sites like Wikipedia have versions a number of languages using subdomains - en.wikipedia.org, de.wikipedia.org and so on. The main benefit of employing a subdomain is that it can have a separate website and its own records, so you're able to even host it on a separate server. The practical use is that one could have a supplementary site, such as an e-learning portal for college students as well as the primary school site. If you use subdomains as an alternative to subfolders, it'll be much easier to perform maintenance or to upgrade a specific website, not mentioning that it will be more secure to have the sites separate from each other.