Robustness is the property of being strong and healthy in constitution. When it is transposed into a system, it refers to the ability of tolerating perturbations that might affect the system's functional body. In the same line robustness can be defined as "the ability of a system to resist change without adapting its initial stable configuration". If the probability distributions of uncertain parameters are known, the probability of instability can be estimated, leading to the concept of stochastic robustness.