Systems whose behavior is not predictable over long periods of time, either from its initial conditions or from its history of inputs. The equations of motion for such a system include threshold values that when breached result in sudden discontinuous changes to qualitatively different states.
See Bifurcation, Catastrophe theory, Chaos, Complex system, Complexity, Control parameter, Determinism, Dissipative system, Dynamical system, Dynamics, Equifinality, Fractals, Isomorphism, Linear dynamical systems, Non-linear dynamics, System