"... a spanning tree T of an undirected graph G is a subgraph that is a tree which includes all of the vertices of G, with minimum possible number of edges."
"A spanning tree of a graph on n vertices is a subset of n-1 edges that form a tree (Skiena 1990, p. 227)."
A spanning tree of an undirected graph on n vertices is a subset of n-1 edges that form a tree.
Given an undirected graph, what are its spanning trees?
Given an undirected graph, how many spanning trees does it have?