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

VTAM
       Virtual Telecommunications Access Method (IBM, SNA)


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

Virtual Telecommunications Access Method
VTAM

   (VTAM) A data communications access method compatible with
   IBM's Systems Network Architecture.

   [More detail?]

   (1995-01-30)