This lecture covers the concepts of entropy and disorder, starting with the definition of entropy according to Shannon. It then explores the relationship between entropy and disorder, illustrating examples of disorder and explaining how the measurement of disorder depends solely on the data of the subsystems. The lecture also delves into the concept of maximum disorder, the additive nature of disorder, and the calculation of disorder in different scenarios. Furthermore, it introduces the theorem related to finding the maximum entropy under certain constraints using the Lagrange multipliers method.