Source : Webster's Revised Unabridged Dictionary (1913)

User \Us"er\, n.
   1. One who uses. --Shak.

   2. (Law) Enjoyment of property; use. --Mozley & W.

Source : WordNet®

user
     n 1: a person who makes use of a thing; someone who uses or
          employs something
     2: a person who uses something or someone selfishly or
        unethically [syn: {exploiter}]
     3: a person who takes drugs [syn: {drug user}, {substance
        abuser}]

Source : Free On-Line Dictionary of Computing

user
     
        1.  Someone doing "real work" with the computer, using
        it as a means rather than an end.  Someone who pays to use a
        computer.  A programmer who will believe anything you tell
        him.  One who asks silly questions without thinking for two
        seconds or looking in the documentation.  Someone who uses a
        program, however skillfully, without getting into the
        internals of the program.  One who reports {bug}s instead of
        just fixing them.  See also {luser}, {real user}.
     
        Users are looked down on by {hackers} to some extent because
        they don't understand the full ramifications of the system in
        all its glory.  The term is relative: a skilled hacker may be
        a user with respect to some program he himself does not hack.
        A LISP hacker might be one who maintains LISP or one who uses
        LISP (but with the skill of a hacker).  A LISP user is one who
        uses LISP, whether skillfully or not.  Thus there is some
        overlap between the two terms; the subtle distinctions must be
        resolved by context.
     
        2.  Any person, organisation, process, device,
        program, {protocol}, or system which uses a service provided
        by others.
     
        The term "{client}" (as in "{client-server}" systems) is
        rather more specific, usually implying two processes
        communicating via some protocol.
     
        [{Jargon File}]
     
        (1996-04-28)