A subdomain is a subdivision of a domain.
For example, if your site mydomain.com have a gallery, you can set up a subdomain with the address gallery.mydomain.com instead mydomain.com/gallery
You can divide the site into different languages such as en.mydomain.com for the English version or de.mydomain.com for the German version.
See our video tutorial on how to create subdomains on your hosting account:
