To make the structure of a CMS-based website a little clearer, a typical technology stack is illustrated here.
Web Host: every website needs to be hosted on a server; the web host provides one or more of the following: domain, fileserver, database, email server
Domain: this is what gives your website its unique ‘address’
User Interface: the user interface (UI) is what the user ‘sees’ and interacts with when accessing the website. For CMS solutions, the administrator logs into the site to make changes
See also: Web Application Technology Stack