This lecture covers the concept of statically indeterminate systems, where some loads or supports are redundant to maintain equilibrium. The instructor explains the approach to solve such systems, including equilibrium, constitutive laws, and kinematic and compatibility conditions. The Displacement Stiffness Method is introduced, where specific displacements are postulated to calculate reaction forces. The lecture also discusses stress concentration, Saint-Venant's principle, and strain energy in one dimension. Various examples are provided to illustrate the application of these concepts.