The Free On-line Dictionary of Computing (30 December 2018):

GT/SQL

    An SQL pre-processor from Greystone Technologies
   which combines MUMPS code with SQL code and generates code
   that can work with a database from both the MUMPS and SQL
   perspectives.  This is often done when a database is to be
   made available in a client/server environment, where the
   MUMPS database serves one or more SQL clients.

   (1995-01-10)