Noun
Lyapunov exponent (plural Lyapunov exponents)
(mathematics) In a dynamical system, a quantity that characterizes the rate of separation of infinitesimally close trajectories.
For example, the maximal Lyapunov exponent (MLE) is most often used because it determines the overall predictability of the system. Source: Internet
In more mathematical terms, the Lyapunov exponent measures the sensitivity to initial conditions. Source: Internet