V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

APPN
       Advanced Peer to Peer Networking (IBM)


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

Advanced Peer-to-Peer Networking
APPN

    (APPN) IBM data communications support
   that routes data in a network between two or more APPC
   systems that need not be adjacent.

   (1995-02-03)