Waterfall

The waterfall model is a relatively linear sequential design approach for certain areas of engineering design. In software development, 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.

The waterfall development model originated in the manufacturing and construction industries; where the highly structured physical environments meant that design changes became prohibitively expensive much sooner in the development process. When first adopted for software development, there were no recognized alternatives for knowledge-based creative work

The Waterfall methodology came about by mistake due to a misunderstanding a 1970 paper which gave it as an example of a methodology along with a comment that states this is a risky method and invites failure. A US Department of Defense standard was published in 1985 with a methodology based on the 1970 paper and it then became widespread.