Waterfall
Waterfall is a linear, sequential software development methodology where progress flows steadily downward through distinct phases like 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 originated in manufacturing and construction industries and was adapted for software development in the 1970s.
Developers should use Waterfall in projects with well-defined, stable requirements, such as government contracts, safety-critical systems (e.g., medical devices), or when regulatory compliance requires extensive documentation. It is suitable for small to medium-sized projects where changes are unlikely, as its rigid structure helps manage costs and timelines predictably, but it can be inflexible for evolving needs.