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

POSIX Threads
Pthreads

    (Pthreads) A POSIX standard API that
   defines a set of C programming language types, functions
   and constants for creating and manipulating pre-emptive
   threads.

   The standard's full name is "POSIX.1c, Threads extensions
   (IEEE Std 1003.1c-1995)".  Implementations are available on
   many Unix-like POSIX-conformant operating systems such as
   FreeBSD, NetBSD, OpenBSD, GNU/Linux, Mac OS X and
   Solaris as well as DR-DOS and Microsoft Windows.

   Pthreads was designed and implemented in the PART Project
   (POSIX / Ada-Runtime Project).

   (2012-04-18)