Waterfall
Waterfall is a linear, sequential project management methodology commonly used in software development, where progress flows steadily downward through distinct phases such as requirements, design, implementation, testing, and maintenance. Each phase must be completed before the next begins, with minimal overlap or iteration, making it highly structured and document-driven. It is often contrasted with agile methodologies, which emphasize flexibility and incremental delivery.
Developers should learn or use Waterfall in environments with well-defined, stable requirements, such as government contracts, safety-critical systems (e.g., aerospace or medical devices), or large-scale infrastructure projects where regulatory compliance and thorough documentation are paramount. It is suitable when changes are costly or disruptive, as it provides clear milestones and predictability, but it can be rigid and less adaptable to evolving needs compared to agile approaches.