Defense in depth is a security strategy that involves applying multiple layers of protection to a system or network to prevent or mitigate attacks. The use of strong authentication, the encryption of Personally Identifiable Information (PII) on database servers, application security reviews, and the encryption of data transmitted across networks are examples of defense in depth measures that can enhance the security of the system or network.
A, C, and D are incorrect because they are not the best terms to describe the security strategy. Data integrity is a property of data that ensures its accuracy, consistency, and validity. Data availability is a property of data that ensures its accessibility and usability. Non-repudiation is a property of data that ensures its authenticity and accountability. While these properties are important for security, they are not the same as defense in depth.