Source : WordNet®

front end
     n : the side that is forward or prominent [syn: {front}, {forepart}]
         [ant: {rear}]

Source : Free On-Line Dictionary of Computing

front end
     
        1. An intermediary computer that does set-up and filtering for
        another (usually more powerful but less friendly) machine (a
        "back end").
     
        2. Software that provides an interface to another program
        "behind" it, which may not be as {user-friendly}.  Probably
        from analogy with hardware front-ends that interfaced with
        {mainframe}s.
     
        [{Jargon File}]