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

OSMVT
       Operating System / Multiprogramming with a Variable number of
Tasks (OS, IBM, S/360, S/370), "OS/MVT"


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

OS/MVT

    One of the IBM operating systems
   associated with the IBM 360, later rereleased with the IBM
   S/370 as OS/VS2.

   [Details?]

   (1999-01-12)