Dynamic Application Security Testing (DAST) is a security testing method that analyzes a running application for vulnerabilities by simulating external attacks. It is a black-box testing technique, meaning it does not require access to the application's internal code or architecture. Instead, DAST tools interact with the application in real-time, probing for security weaknesses from an attacker’s perspective. Overall, DAST is a crucial component of a comprehensive security testing strategy, providing valuable insights into an application's security posture by simulating real-world attacks and identifying vulnerabilities in running applications.