Development activities are carried out sequentially, with some overlap but little or no iteration between them. User requirements are defined, and the entire system is designed, built, and tested for ultimate delivery at a single point in time. A document-driven approach that works best for highly precedence systems with consistent requirements.
The waterfall model is also known as the linear and sequential model because the flow of activities in this model is, as the name implies, linear and sequential. In this model, software development activities move to the next phase only after the current phase's activities are completed. However, unlike a waterfall, there is no way to return to the previous stage.