Administrator

An administrator, also known as an admin, root, or superuser, is a user account with higher level privileges to manage the system. User permissions were typically not assigned in classic Mac OS and became commonplace with the adoption of Mac OS X (now macOS), like other Unix-based operating systems.

macOS
In macOS, an administrator can add and manage other users, install apps, and change settings in the System Preferences. When a Mac is being set up, the first user account to be created is provided administrator privileges. A modern Mac can have multiple administrators. An administrator can create new ones, and convert standard users to administrators.

Administrators are advised by Apple to avoid using automatic login for security reasons. Otherwise, a stranger could simply restart the Mac and gain access with administrator privileges. To keep a Mac secure, users are advised not to share administrator names nor passwords.

iOS
Apple's handheld mobile consumer devices, such as iPhones and iPod touches, assign access to a single user through an Apple ID. Apple advises that the Apple ID and associated data should be deleted before the device is sold or passed on to another user. Apple ID users on iOS devices are not provided full administrator privileges to reduce the possibility that they would corrupt the system and render it non-functional. Jailbreaking is the process of escalating the user privileges to gain more access to the device to add features or software not sanctioned by the manufacturer. Such activity, if detected, can void the warranty of the device.

iPadOS
Starting in iOS 13.4, organizations can set up a shared iPad for use by multiple Apple ID users through temporary sessions. Such devices can be remotely managed by a MDM (mobile device management) administrator.

History
Activities performed by a system administrator (or "admin", "sysadmin", "site admin") historically included monitoring the security configuration, managing allocation of user names and passwords, monitoring disk space and other resource management on a shared system, such as performing backups, and setting up new hardware and software. System administrators often also assist other users, though in a large organization this may be a separate job.