black art

black art n.  A collection of arcane, unpublished, and (by
   implication) mostly ad-hoc techniques developed for a particular
   application or systems area (compare {black magic}).  VLSI
   design and compiler code optimization were (in their beginnings)
   considered classic examples of black art; as theory developed they
   became {deep magic}, and once standard textbooks had been
   written, became merely {heavy wizardry}.  The huge proliferation
   of formal and informal channels for spreading around new
   computer-related technologies during the last twenty years has made
   both the term `black art' and what it describes less common than
   formerly.  See also {voodoo programming}.