Waterfall is a sequential delivery model that moves through fixed phases, such as requirements, design, implementation, testing, and release. Each stage ends with a formal handoff and approval before the next one begins. This makes the process predictable and easy to audit, which is why it is still common in regulated environments and in security programs that need clear documentation, change control, and sign-off.
In cyber security, Waterfall matters because it shapes how defenses are planned and deployed. It can support strong governance for secure architecture reviews, compliance evidence, and controlled rollouts. But its rigidity can also slow patching, incident-response improvements, and adaptation to new threats. Attackers benefit when organizations move slowly through approvals, leaving known weaknesses unpatched. For that reason, many teams combine Waterfall controls with more iterative security practices so they can keep traceability without sacrificing response speed.