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

IEN
       Internet Experiment Notebook (predecessor, RFC)


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

IEN
       Internet Engineering Notes


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

Internet Experiment Note
IEN

   (IEN) A series of reports pertinent to the Internet.  IENs
   were published in parallel to RFCs and are no longer active.

   See also Internet-Draft, Request For Comments.

   (1994-12-08)