A Minimum Spanning Tree (MST) is a subset of the edges of a connected, weighted, and undirected graph. It connects all the vertices together without any cycles and with the minimum possible total edge weight. The MST includes all the vertices of the original graph but only a subset of the edges.

To understand this, imagine you have a network of cities connected by roads, each with a different length (or cost). The goal is to connect all cities with the shortest total road length without forming any loops. The MST provides this optimal solution.