This lecture covers the concept of stationary sources, focusing on the Green-Blue source and the Weekly-Coin-Flip source. It explains how to find probabilities, entropies, and regularity of these sources. The instructor discusses the definition of a stationary source and its implications, such as the equality of statistics for shifted blocks. The lecture delves into the proof that stationary sources are regular and explores the relationship between source entropy rate and average codeword length. The Cesàro Means theorem is used to establish the convergence of entropy values. Finally, the lecture concludes with a challenge involving determining the odd ball among 14 billiard balls with minimal weightings.