The Waterfall Model is a linear and sequential approach to software development, where each phase of the development process (requirements, design, implementation, testing, and maintenance) is completed before moving on to the next. This model assumes that requirements are well understood and that changes are not likely to occur once development begins. Each phase must be completed before moving on to the next, and there is little opportunity for revisiting or revising previous phases. This model is useful for projects with well-defined requirements and predictable outcomes, but may not be suitable for projects that are more complex or require more flexibility.