demon

demon n.  1. [MIT] A portion of a program that is not
   invoked explicitly, but that lies dormant waiting for some
   condition(s) to occur.  See {daemon}.  The distinction is that
   demons are usually processes within a program, while daemons are
   usually programs running on an operating system.  2. [outside MIT]
   Often used equivalently to {daemon} -- especially in the
   {{UNIX}} world, where the latter spelling and pronunciation is
   considered mildly archaic.

   Demons in sense 1 are particularly common in AI programs.  For
   example, a knowledge-manipulation program might implement inference
   rules as demons.  Whenever a new piece of knowledge was added,
   various demons would activate (which demons depends on the
   particular piece of data) and would create additional pieces of
   knowledge by applying their respective inference rules to the
   original piece.  These new pieces could in turn activate more
   demons as the inferences filtered down through chains of logic.
   Meanwhile, the main program could continue with whatever its
   primary task was.