Source : Free On-Line Dictionary of Computing

spiral model
     
         A {software life-cycle} model which supposes
        incremental development, using the {waterfall model} for each
        step, with the aim of managing risk.  In the spiral model,
        developers define and implement features in order of
        decreasing priority.
     
        [Barry Boehm, "A Spiral Model of Software Development and
        Enhancement", ACM SIGSOFT Software Engineering Notes, August
        1986].
     
        [Barry Boehm "A Spiral Model of Software Development and
        Enhancement" IEEE Computer, vol.21, #5, May 1988, pp 61-72].
     
        [Better explanation?]
     
        (1997-11-23)