Source : Free On-Line Dictionary of Computing

copying garbage collection
     
        A {garbage collection} method where memory is divided into two
        equal halves, known as the "from space" and "to space".
        Garbage collection copies active cells from the from space to
        the to space and leaves behind an invisible pointer (an
        "indirection") from the old position to the new copy.  Once
        all active cells have been copied in one direction, the spaces
        are swapped and the process repeated in the opposite
        direction.