Source : Free On-Line Dictionary of Computing

Waterfall Model
     
         A {software life-cycle} or {product life-cycle}
        model, described by W. W. Royce in 1970, in which development
        is supposed to proceed linearly through the phases of
        {requirements analysis}, design, implementation, testing
        (validation), integration and maintenance.  The Waterfall
        Model is considered old-fashioned or simplistic by proponents
        of {object-oriented design} which often uses the {spiral
        model} instead.
     
        Earlier phases are sometimes called "upstream" and later ones
        "downstream".
     
        Compare: {iterative model}.
     
        [W. W. Royce, "Managing the Development of Large Software
        Systems", Proceedings of IEEE WESCON, August 1970].
     
        (1997-11-23)