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

symmetric multiprocessing
symmetric multiprocessor

    (SMP) Two or more similar processors connected
   via a high-bandwidth link and managed by one operating
   system, where each processor has equal access to I/O devices.
   This is in contrast to the "compute server" kind of
   parallel processor where a front-end processor handles all
   I/O to disks, terminals and local area network etc.

   The processors are treated more or less equally, with
   application programs able to run on any or perhaps all
   processors in the system, interchangeably, at the operating
   system's discretion.  Simple MP usually involves assigning
   each processor to a fixed task (such as managing the file
   system), reserving the single main CPU for general tasks.

   OS/2 currently supports so-called HMP (Hybrid
   Multiprocessing), which provides some elements of symmetric
   multiprocessing, using add-on IBM software called MP/2.  OS/2
   SMP was planned for release in late 1993.

   (1995-03-19)