Waterfall approach was first Process Model to be introduced and followed widely in Software Engineering to ensure success of the project. In "The Waterfall" approach, the whole process of software development is divided into separate process phases.
The phases in Waterfall model are: Requirement Specifications phase, Software Design, Implementation and Testing & Maintenance. All these phases are cascaded to each other so that second phase is started as and when defined set of goals are achieved for first phase and it is signed off, so the name "Waterfall Model". All the methods and processes undertaken in Waterfall Model are more visible.
A Requirements phase, in which the requirements for the software are gathered and analyzed. Iteration should eventually result in a requirements phase that produces a complete and final specification of requirements. –
A Design phase, in which a software solution to meet the requirements is designed. This may be a new design, or an extension of an earlier design.An Implementation and Test phase, when the software is coded, integrated and tested.A Review phase, in which the software is evaluated, the current requirements are reviewed, and changes and additions to requirements proposed.