My question is about terminology.
I am interested in the reason why spanning trees are called this way. English is not my native language so maybe there is something that I don't see and a native speaker would see.
Why are spanning trees of a graph called like this "spanning" ?
In mathematics, the word "span" is used about one thing that can reach every part of a (possibly) larger thing, under a suitable definition of "reach". A tree is a special kind of graph. So a spanning tree of a given graph is a smaller graph (a so-called subgraph) which reaches every node of the original graph, but at the same time fulfills the requirements of a tree.