Verification and Validation are terms associated with having/gaining confidence in an implementation such as a model, a piece of software, or a design in general.
Verification is the process of determining whether an implementation behaves the way the designers intended it to behave.
Validation is a process of determining whether an implementation behaves as the customer would have wanted it to behave if he had been able to correctly specify what he wanted.
Introduction
Examples of Verification and Validation.
Methods of Verification
Methods of Validation
Complications in Application of Verification and Validation Techniques
The term vulnerability of a system relates to survivability in the light of a threat of some sort.