Which stage is NOT part of the Waterfall Model?

In the context of the Waterfall Model, which is a linear and sequential approach to software development, User Acceptance Testing is typically not classified as a distinct stage within the model. The stages usually include requirements definition, design and development, integration, and system testing, followed by deployment. The process emphasizes a structured flow where each stage must be completed before moving on to the next one.

User Acceptance Testing, while crucial for validating that the system meets user requirements and is ready for deployment, is considered part of the general testing phase rather than a standalone stage in the model itself. This phase usually occurs after system testing has been completed and is essential for ensuring that the final product aligns with the users' needs but is not explicitly listed as one of the formal phases in the original Waterfall framework.

Recognizing the distinct phases of the Waterfall Model helps clarify the roles and responsibilities within the software development lifecycle, illustrating how requirements transition through to deployment, and highlighting where user testing fits in the broader context.