A subdomain is the part of the web address that's before a domain and you have most likely seen a lot of subdomains while exploring the Web. As an illustration, many websites like Wikipedia have versions a number of languages using subdomains - en.wikipedia.org, de.wikipedia.org and so on. The best thing about using a subdomain is that it can have an independent site and its own records, so you are able to even host it on another server. The practical use is that one could have a supplementary website, such as an e-learning portal for college students as well as the main school site. If you are using subdomains rather than subfolders, it'll be much easier to perform maintenance or to upgrade a certain website, not mentioning that it'll be more secure to have the sites separate from each other.