A user with the administrator user role is capable of editing all content, plugins, themes, users and settings on a WordPress installation. They can add new users, delete the existing theme, add new plugins and make whatever changes they want to the content on the site.
Because of their extensive capabilities, it’s a good idea to limit the number of administrator users on a WordPress installation to as few as possible. If a user only needs to edit content on the site, a less capable user role, like editor, is a better choice. You should also take extra care with password strength and other security measures for administrator users.
On multisites – networks consisting of multiple WordPress websites – there is one user role more capable than the administrator, and that is the super admin. Super admins have the capability to add and delete sites from the network, in addition to having the same capabilities as administrators on each individual site. Regular administrators can manage all content and settings on network sites that they are assigned access to, but they can’t manage the network as a whole.