The Waterfall model is a linear process model, in which each phase produces an approved work product that is then used by the next phase. The work product flows into the next phase, and this continues until the end of the process, like a waterfall. There are modified variants of the Waterfall model that allow flows to prior phases, but the dominant flow is still forward and linear.

Pros and cons

Pros:

• easy to understand
• clearly defines deliverables and milestones
• emphasizes the importance of analysis before design, and design before implementation
• can be adopted within teams using more sophisticated processes, for well-specified parts of the product that can be outsourced

Cons:

• not very adaptable to change
• testing occurs late in the process, and defects found late tend to be more difficult and costly to fix
• the client does not see the finished product until everything is virtually complete