Source : WordNet®

black box
     n : equipment that records information about the performance of
         an aircraft during flight

Source : Free On-Line Dictionary of Computing

black box
     
         An {abstraction} of a device or system in which only
        its externally visible behaviour is considered and not its
        implementation or "inner workings".
     
        See also {functional testing}.
     
        (1997-07-03)