From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :
SVR4
System V Release 4 (Unix, OS, AT&T)
From The Free On-line Dictionary of Computing (30 December 2018) :
SVR4
AT&T/{USL">AT&T/{USL Unix System V Release 4.
(1995-03-28)