Fuzzing is a testing technique where invalid or random data is inputted into a system to find vulnerabilities, crashes, or unexpected behaviors. It's commonly used in software security to identify flaws that could lead to security breaches. According to CompTIA's CySA+ curriculum, fuzzing is a dynamic testing method for exposing application weaknesses. Options like static testing (B) involve analyzing code without execution, while reverse engineering (A) and debugging (D) involve different methodologies for understanding or fixing code, not intentionally stressing it.