Source : Free On-Line Dictionary of Computing

space complexity
     
         The way in which the amount of storage space
        required by an {algorithm} varies with the size of the problem
        it is solving.  Space complexity is normally expressed as an
        order of magnitude, e.g. O(N^2) means that if the size of the
        problem (N) doubles then four times as much working storage
        will be needed.
     
        See also {computational complexity}, {time complexity}.
     
        (1996-05-08)