Terminology

TREE
Any graph that is connected AND has no circuits is called a Tree.

THIS IS A TREE
A connected graph with no circuits.

THIS IS NOT A TREE
This graph contains a circuit.

 

SPANNING TREE
A tree inside of a connected graph that includes every vertex of the original graph is called a Spanning Tree.

The tree (represented by the blue edges) within the above connected graph IS a SPANNING TREE since it is a tree and it includes every vertex of the graph. The tree (represented by the blue edges) within the above connected graph IS NOT a SPANNING TREE since it does not include every vertex of the graph.

 

MINIMUM SPANNING TREE
In a weighted connected graph, a spanning tree with the least total weight is called a Minimum Spanning Tree.

 

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