From Joomla! Documentation
Joomla! maintains two primary classifications of user groups. The classifications are primarily Frontend (site) and Backend (Administration) user groups. Frontend users are only allowed to log in using the public facing side of the website. Backend users are allowed to log in on the administrative side of the web site. As a result these users are also referred to as administrative users or admins.
Administrative logins are available by default at https://example.org/administrator.
Backend Users are Further Separated into Two Groups
- Super Users
The most privileged of these users belong to the Super Users group. Super Users have the highest privilege level and can make changes or add new features or content to any section of a Joomla! site.
Points to Note on Super Users
- The default Super Users is admin and is installed with every Joomla! site.
- Super Users are able to log in on the Frontend or Backend of the site.
- A Joomla! site may have more than one designated Super User.