What is Waterfall?

Waterfall is a sequential, non-iterative design process, used in software development and other fields, where progress is seen as flowing steadily downwards (like a waterfall) through the phases of conception, initiation, analysis, design, construction, testing, production/implementation and maintenance. Each phase must be completed fully before the next phase can begin. It is a rigid approach, often criticized for its lack of flexibility and difficulty in accommodating changes once a phase is complete.