This lecture covers the probabilistic description of turbulence, focusing on the stochastic nature of turbulent signals and the limitations of deterministic chaos in predicting the behavior of nonlinear dynamical systems. Through examples like the Lorenz equations, the instructor explains the sensitivity to initial conditions and the need for a stochastic approach despite the deterministic dynamics. The presentation includes discussions on individual measurements, statistics, and the reproducibility of results, highlighting the challenges in accurately predicting turbulent behavior.