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Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   avatar
   av
      1. <chat, virtual reality> An image representing a user in a
      multi-user virtual reality (or VR-like, in the case of
      Palace) space.
      2. (CMU, Tektronix) root, superuser.  There are quite a
      few Unix computers on which the name of the superuser
      account is "avatar" rather than "root".  This quirk was
      originated by a CMU hacker who disliked the term
      "superuser", and was propagated through an ex-CMU hacker at
      Tektronix.
      [Jargon File]
      (1997-09-14)