The Jargon File (version 4.4.7, 29 Dec 2003):

wheel bit
 n.

    A privilege bit that allows the possessor to perform some restricted
    operation on a timesharing system, such as read or write any file on the
    system regardless of protections, change or look at any address in the
    running monitor, crash or reload the system, and kill or create jobs and
    user accounts. The term was invented on the TENEX operating system, and
    carried over to TOPS-20, XEROX-IFS, and others. The state of being in a
    privileged logon is sometimes called wheel mode. This term entered the Unix
    culture from TWENEX in the mid-1980s and has been gaining popularity there
    (esp. at university sites). See also root.


The Free On-line Dictionary of Computing (30 December 2018):

wheel bit

   A privilege bit that allows the possessor to perform some
   restricted operation on a time-sharing system, such as read
   or write any file on the system regardless of protections,
   change or look at any address in the running monitor, crash or
   reload the system, and kill or create jobs and user accounts.
   The term was invented on the TENEX operating system, and
   carried over to TOPS-20, XEROX-IFS, and others.  The state of
   being in a privileged logon is sometimes called "wheel mode".
   This term entered the Unix culture from TWENEX in the
   mid-1980s and has been gaining popularity there (especially at
   university sites).  See also root.