Robustness is an important characteristic of a control system, as it determines how well the system can perform in the presence of uncertainties and disturbances. A robust control system is able to maintain stability and optimal performance over a wide range of parameter variations.

Sensitivity:
Sensitivity refers to how the system responds to changes in its parameters. A control system with low sensitivities means that it is less affected by variations in its parameters. In other words, small changes in the system's parameters do not result in significant changes in the system's performance. Low sensitivities are desirable because they indicate that the system is less vulnerable to uncertainties and disturbances.

Stability:
Stability is a fundamental requirement for any control system. A stable control system maintains a desired output in the presence of disturbances and uncertainties. It ensures that the system does not exhibit oscillatory or diverging behavior, which can lead to instability. A control system that is stable over a wide range of parameter variation is considered to be robust.

Robustness:
The combination of low sensitivities and stability makes a control system robust. When a control system has low sensitivities, it means that it is not highly influenced by parameter variations. This allows the system to maintain its desired performance even when there are changes in the parameters. Additionally, when a control system is stable over a wide range of parameter variation, it means that it can adapt to different operating conditions without losing stability. This adaptability is a key characteristic of a robust control system.

Conclusion:
In conclusion, a control system is said to be robust when it has both low sensitivities and stability over a wide range of parameter variation. This means that the system is able to maintain its desired performance despite uncertainties and disturbances. Robust control systems are desirable because they are more reliable and can handle a variety of operating conditions.