Source : WordNet®

scalability
     n : the quality of being scalable

Source : Free On-Line Dictionary of Computing

scalability
     
        How well a solution to some problem will work when the size of
        the problem increases.
     
        For example, a central {server} of some kind with ten
        {client}s may perform adequately but with a thousand clients
        it might fail to meet response time requirements.  In this
        case, the average response time probably scales linearly with
        the number of clients, we say it has a {complexity} of O(N)
        ("order N") but there are problems with other complexities.
        E.g. if we want N nodes in a network to be able to communicate
        with each other, we could connect each one to a central
        exchange, requiring O(N) wires or we could provide a direct
        connection between each pair, requiring O(N^2) wires (the
        exact number or formula is not usually so important as the
        highest power of N involved).
     
        (1995-03-29)