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

Application environment specification

    (AES) A set of specifications from OSF for
   programming and user interfaces, aimed at providing a
   consistent application environment on different hardware.  It
   includes "O/S" for the operating system (user commands and
   program interfaces), "U/E" for the User Environment (Motif),
   and "N/S" for Network services.

   [Reference?]

   (1994-12-07)