This lecture covers the concept of spanning trees in connected undirected graphs, defining them as trees that include all nodes with no cycles. The instructor explains the Minimum Spanning Tree (MST) problem, where the goal is to find a tree of minimum cost. Various formulations and algorithms, such as Cutset Formulation and Gomory Cutting Planes, are presented to solve the MST problem efficiently. The lecture also discusses the importance of good formulations and the complexity of problems in optimal decision-making.