An administrator account is a user account on an operating system which allow make changes that can affect other users (including, but not limited to, the creation and restriction of user accounts), change operating system options (including security settings), install software and drivers, access all files.
A type of user account on an operating system which will typically allow all functions to be performed to a computer, including (but not limited to) the creation and restriction of user accounts, installing software or drivers, or changing operating system options. On WordPress CMS, it's the user role that has the highest privileges and capabilities.