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

Synthesizer Specification Language

   (SSL) A specification language based on term algebra and
   attribute grammars.  SSL is used by the Synthesizer
   Generator, a generator for language-based editors such as
   the Cornell Program Synthesizer.

   ["Generating Language Based Environments", T. Reps, MIT Press
   1984].

   (1994-12-16)