sorry...
en.wikipedia.org/wiki/POSIX :
The SUS emerged from a project, begun circa
1985, to standardise the
application program interface for software designed to run on variants of the UNIX operating system. This became IEEE 1003, or
POSIX — a name given to it by
Richard Stallman, in request for a memorable name for the standard — which loosely stood for
Portable Operating System Interface.