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

Win32s

    A free extension for Microsoft Windows,
   released by Microsoft.  Win32s is a software layer on top of
   Windows which allows 32-bit applications (e.g. Mosaic) to
   run on Windows.  Both stand-alone Windows and Windows for
   Workgroups run as 16 bit, and both can use Win32s to run
   32-bit applications.

   (1996-07-08)