WordNet (r) 3.0 (2006):

system administrator
    n 1: a person in charge of managing and maintaining a computer
         system of telecommunication system (as for a business or
         institution)

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

system administration
admin
sysadmin
system administrator

    Activities performed by a system administrator (or
   "admin", "sysadmin", "site admin") such as monitoring security
   configuration, managing allocation of user names and
   passwords, monitoring disk space and other resource use,
   performing backups, and setting up new hardware and
   software.

   system administrators often also help users, though in a large
   organisation this may be a separate job.

   Compare postmaster, sysop, system management, systems
   programmer.

   [Other tasks?]

   (1999-05-02)