This lecture by the instructor covers the topic of Brillouin scattering, a powerful tool in photonics. It explains how material density fluctuations impact light, the physics behind inelastic scatterings, and the optical effects due to these scatterings. The lecture delves into the principles of Brillouin stimulated scattering, the spectral characteristics of inelastic scatterings, and the mechanisms behind stimulated scatterings. It also explores the applications of Brillouin scattering in optical fibers, amplifiers, sensing, optical storage, and signal processing. The lecture concludes with discussions on the limitations and advancements in Brillouin scattering technology.