Source : Free On-Line Dictionary of Computing

reference counting
     
         A {garbage collection} technique where each
        {memory cell} contains a count of the number of other cells
        which point to it.  If this count reaches zero the cell is
        freed and its {pointers} to other cells are followed to
        decrement their counts, and so on {recursively}.
     
        This technique cannot cope with {circular data structures}.
        Cells in such structures refer (indirectly) to themselves and
        so will never have a zero reference count.  This means they
        would never be reclaimed, even when there are no references
        from outside the structure.
     
        (1995-02-22)