Which of the following is NOT a type of performance testing?

Performance testing is primarily concerned with evaluating how a system performs under certain conditions, which typically includes measuring response times, ensuring stability, and checking the system's behavior under expected and extreme loads.

Load testing assesses how well a system handles expected user loads, while stress testing determines the system’s limits by subjecting it to excessive loads until it fails. Endurance testing, often known as soak testing, verifies the system's performance over an extended period to evaluate its stability and memory usage over time.

On the other hand, exploratory testing is a technique where testers explore the application without predefined test cases, focusing on discovering defects through interactive and informal testing. It does not fit within the framework of performance testing as it does not specifically assess performance metrics but rather seeks to find unexpected behavior and defects in the software through ad-hoc testing methods. Thus, exploratory testing is the option that does not belong among the types of performance testing.