*In physics, a fluctuation is a variation in an extensive or intensive quantity, such as energy, density or voltage, from its spatial or temporal average. The mean-square fluctuation langle X angle^2 is equivalent to the variance in statistics. If X_i is the ith data point of X,the mean-square fluctuation is calculated as » X_i = langle X_i^2 angle - langle X_i angle ^2 In thermodynamics, a fluctuation is a perturbation in an equilibrium or far-from-equilibrium thermodynamic system. See also F… (More on Fluctuation)