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

FSL

   Formal Semantics Language.

   A language for compiler writing.

   ["A Formal Semantics for Computer Languages and its Application
   in a Compiler-Compiler", J.A. Feldman, CACM 9(1) (Jan 1966)].

   [Sammet 1969, p. 641].

   (1995-01-23)