Source : Free On-Line Dictionary of Computing

Uninterruptible Power Supply
     
         (UPS) A battery powered power supply that is
        guaranteed to provide power to a computer in the event of
        interruptions in the incoming electrical power.  Different
        rating UPSs will provide power for different lengths of time.
     
        Modern UPSs connect to the computer's {serial port} and
        provide information such as battery time remaining, allowing
        the computer to shut down {gracefully} before complete loss of
        power.
     
        (1996-12-11)