Answer
A spanning tree of a graph is a subgraph which contains all of the original vertices, is connected, and does not contain any circuits.
Work Step by Step
A graph has vertices and edges. A subgraph is a graph with vertices and edges which are chosen from the set of vertices and edges in the original graph.
A spanning tree of a graph is a subgraph which contains all of the original vertices, is connected, and does not contain any circuits.