legacy system
legacy
legacy code
legacy software

    A computer system or application program which
   continues to be used because of the cost of replacing or
   redesigning it and often despite its poor competitiveness and
   compatibility with modern equivalents.  The implication is
   that the system is large, monolithic and difficult to modify.

   If legacy software only runs on antiquated hardware the cost
   of maintaining this may eventually outweigh the cost of
   replacing both the software and hardware unless some form of
   emulation or backward compatibility allows the software to
   run on new hardware.

   (1998-08-09)