“Resilience is the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks. … The notion of speed of return to equilibrium (Pimm 1991) leads to what has been termed “engineering resilience” (Holling 1996) and, although related to one aspect of “ecological resilience,” cannot be considered as the measure of resilience. Because of the possibility of multiple stable states, when considering the extent to which a system can be changed, return time doesn’t measure all of the ways in which a system may fail—permanently or temporarily—to retain essential functions. It is also important to bear in mind that “systems” consist of nested dynamics operating at particular organizational scales—“sub-systems,” as it were, of households to villages to nations, trees to patches to landscapes.
There are four crucial aspects of resilience. The first three can apply both to a whole system or the sub-systems that make it up.

1. Latitude: the maximum amount a system can be changed before losing its ability to recover (before crossing a threshold which, if breached, makes recovery difficult or impossible).
2. Resistance: the ease or difficulty of changing the system; how “resistant” it is to being changed.
3. Precariousness: how close the current state of the system is to a limit or “threshold.”
4. Panarchy: because of cross-scale interactions, the resilience of a system at a particular focal scale will depend on the influences from states and dynamics at scales above and below. For example, external oppressive politics, invasions, market shifts, or global climate change can trigger local surprises and regime shifts.”

Walker, B., C. S. Holling, S. R. Carpenter, and A. Kinzig. 2004. Resilience, adaptability and transformability in social–ecological systems. Ecology and Society 9(2): 5.