Definition
Defence in Depth is a security design strategy that uses multiple complementary protection mechanisms so that defeating one safeguard does not automatically compromise the complete system.
Human Explanation
Instead of relying on one safeguard, a system is protected by several independent layers that make a successful Attack more difficult.
Why it Matters
No individual safeguard is completely reliable. Several layers significantly increase system resilience.
Conceptual Boundary
Defence in Depth does not mean using as many safeguards as possible. Layers should complement one another and address different Threats.
Practical Perspective
Effective security results from combining architecture, people, processes and technology rather than relying on one best solution.