A subdomain is the section of the web address that is before a domain name and you have quite possibly seen a lot of subdomains while exploring world wide web. As an illustration, many websites like Wikipedia have versions a number of languages using subdomains - en.wikipedia.org, de.wikipedia.org and so forth. The main benefit of using a subdomain is that it can have a separate site and its own records, so you are able to even host it on another server. The practical use is that you can have a supplementary website, like an e-learning portal for college students as well as the main school site. If you are using subdomains rather than subfolders, it will be much easier to perform maintenance or to upgrade a particular website, not mentioning that it's going to be more secure to have the websites separate from each other.