Resiliency is typically understood as the capacity of a system to maintain functionality given some perturbation.  When a system is subject to some sort of perturbation or disturbance, it responds by moving away from its initial state. The tendency of a system to remain close to its equilibrium state, despite that disturbance, is termed its resistance. On the other hand, the speed with which it returns to its initial state after disturbance may be understood as its resilience.