This lecture covers the concept of quasicovexity in the context of variational calculus, focusing on x-independent and x-dependent integrands. The instructor explains the necessary conditions for weak and strong quasicovexity, illustrating with propositions and proofs. The lecture delves into the application of Jensen's inequality and the behavior of minimizers in the context of functional optimization. It concludes with a discussion on Young measures and the implications of quasicovexity on the minimization process.