Minimum Spanning Tree
A minimum spanning tree (MST) is kind of tree
A subset of the edges of a connected, edge-weighted graph that connects all the vertices together without any cycles and with the minimum possible total edge weight.
It is a way of finding the optimal way to connect all the vertices in the tree.
Example is a telecommunications company trying to lay cable in a new neighborhood. If it is constrained to bury the cable only along certain paths (e.g. roads), then there would be a graph containing the points (e.g. houses) connected by those paths.