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

System Management Mode
SMM

    (SMM) A reduced power consumption state provided by
   some Intel microprocessors.  When a CPU enters SMM it
   saves its current state in a special area of static RAM
   called SMRAM (System Management RAM) and then runs a
   program, also stored in SMRAM, the SMM handler.

   SMM is implemented in all Intel "SL" suffixed CPUs.  In June
   1993, Intel announced it was discontinuing its SL range and
   instead making all its current processors SL enhanced.

   See also Auto Idle.

   (1994-11-09)