Threat modeling is the testing technique that enables the designer to develop mitigation strategies for potential vulnerabilities. Threat modeling is a method of identifying, analyzing, and prioritizing the threats and vulnerabilities that may affect a system or an application. Threat modeling can help the designer to understand the attack surface, the attack vectors, the attack scenarios, and the impact and likelihood of the attacks. Threat modeling can also help the designer to develop mitigation strategies for the potential vulnerabilities, such as applying security controls, implementing security best practices, or redesigning the system or the application.
Threat modeling can be performed at any stage of the system development life cycle (SDLC), but it is most effective when done early and iteratively. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 8: Software Development Security, page 441. Free daily CISSP practice questions, Question 2.