Source : Free On-Line Dictionary of Computing

Advanced Power Management
     
         (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)