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

STREAMS

    A collection of system calls, kernel
   resources, and kernel utility routines that can create, use,
   and dismantle a stream.  A "stream head" provides the
   interface between the stream and the user processes.  Its
   principal function is to process STREAMS-related user system
   calls.  A "stream module" processes data that travel bewteen
   the stream head and driver.  The "stream end" provides the
   services of an external input/output device or an internal
   software driver.  The internal software driver is commonly
   called a pseudo-device driver.

   The STREAMS concept has been formalised in Unix System V.
   For example, SVR4 implements sockets and pipes using
   STREAMS, resulting in pipe(2) openning bidirectional pipes.

   [IBM AIX 3.2 Communication Programming Concepts, SC23-2206-03].

   (1999-06-29)