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

OSVS2
       (IBM, MVS), "OS/VS2"


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

OSVS2
       Operating System / Virtual System - 2 (OS, IBM, S/370), "OS/VS-2"


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

OS/VS2
Single Virtual Storage
SVS

    An operating system from IBM, released
   with the IBM S/370 and originally known as OS/MVT.  OS/VS2
   R1 was known as SVS (Single Virtual Storage) as it had a
   single 16 MB virtual address space.  OS/VS2 R2 was known as
   MVS - Multiple Virtual Storage.

   (1999-01-13)