The Free On-line Dictionary of Computing (19 January 2023):

Advanced Power Management
APM
green monitor

    (APM) A feature of some displays, usually but not
   always, on laptop computers, which turns off power to the
   display after a preset period of inactivity to conserve
   electrical power.  Monitors with this capability are usually
   refered to as "green monitors", meaning environmentally
   friendly.

   Not to be confused with a screen blanker which is software
   that causes the display to go black (by setting every pixel
   to black) to prevent burn-in.

   (1997-08-25)