Source : Free On-Line Dictionary of Computing

Turing tar-pit
     
        A place where anything is possible but nothing of interest is
        practical.  {Alan M. Turing} helped lay the foundations of
        computer science by showing that all machines and languages
        capable of expressing a certain very primitive set of
        operations are logically equivalent in the kinds of
        computations they can carry out, and in principle have
        capabilities that differ only in speed from those of the most
        powerful and elegantly designed computers.  However, no
        machine or language exactly matching Turing's primitive set
        has ever been built (other than possibly as a classroom
        exercise), because it would be horribly slow and far too
        painful to use.
     
        A "Turing tar-pit" is any computer language or other tool that
        shares this property.  That is, it's theoretically universal
        but in practice, the harder you struggle to get any real work
        done, the deeper its inadequacies suck you in.  Compare
        {bondage-and-discipline language}.
     
        A tar pit is a geological occurence where subterranean tar
        leaks to the surface, creating a large puddle (or pit) of tar.
        Animals wandering or falling in get stuck, being unable to
        extricate themselves from the tar.  La Brea, California, has a
        museum built around the fossilized remains of mammals and
        birds found in such a tar pit.
     
        [{Jargon File}]
     
        (1998-06-27)