Waterfall model

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The waterfall model is a breakdown of development activities into linear sequential phases, meaning they are passed down onto each other, where each phase depends on the deliverables of the previous one and corresponds to a specialization of tasks.^[1] The approach is typical for certain areas of engineering design. In software development,^[1] it tends to be among the less iterative and flexible approaches, as progress flows in largely one direction ("downwards" like a waterfall) through the phases of conception, initiation, analysis, design, construction, testing, deployment and maintenance.^{[2][better source needed]} The waterfall model is the earliest SDLC approach that was used in software development.^{[citation needed]}

The waterfall development model originated in the manufacturing and construction industries,^{[citation needed]} where the highly structured physical environments meant that design changes became prohibitively expensive much sooner in the development process. ^{[citation needed]} When first adopted for software development, there were no recognized alternatives for knowledge-based creative work.^{[3][better source needed]}