Source : Free On-Line Dictionary of Computing

grep
     
          A {Unix} command for
        searching files for lines matching a given {regular
        expression} (RE).  Named after the {qed}/{ed} editor
        subcommand "g/re/p", where re stands for a regular expression,
        to Globally search for the Regular Expression and Print the
        lines containing matches to it.  There are two other variants,
        fgrep which searches only for fixed strings and {egrep} which
        accepts extended REs but is usually the fastest of the three.
     
        Used by extension to mean "to look for something by pattern".
        When browsing through a large set of files, one may speak of
        "grepping around".  "Grep the bulletin board for the system
        backup schedule, would you?"  See also {vgrep}.
     
        [{Jargon File}]