# Tree : Forest :: Path :?

A forest is a collection of trees.

Is there a similar notion for paths? e.g., a _______ is a collection of paths.

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Not that I know of. You can call it a "path forest". – Yuval Filmus Feb 25 '14 at 0:44
I haven't heard of a suitable term either. Just to speculate wildly, I conjecture that it's because "tree" and "path" do not refer to the same sort of object. A tree is a type of graph (connected acyclic) and a forest is where we drop the acyclic part. A path, at the basic level, is a sort-of-ordered subset of the vertices/edges (depending on how you want to define it) of a graph, and we just overload the term to mean a graph that doesn't have any other vertices or edges either. Then with this view there's no "collection of paths", and by inertia we haven't created one since. – Luke Mathieson Feb 25 '14 at 0:51
@LukeMathieson I don't buy your argument that a path isn't a "real" graph at all. Paths are perfectly good graphs in their own right; the fact that their structure is so simple that they can be uniquely specified by listing their vertices in order doesn't affect that. – David Richerby Feb 25 '14 at 1:29
@DavidRicherby, I wasn't saying that they're not "real" graphs, I was speculating wildly about the historical reason we don't seem to have a neat, widely known term for disjoint union of paths. – Luke Mathieson Feb 25 '14 at 1:31
@LukeMathieson: You probably also meant that a forest is where you drop the condition of being connected. In any case, even if there are historical reasons why collections of paths were not given a name, surely by the time people started studying path covers this should not longer have been true. One could just as easily ask: Spanning Forest : Path cover :: Forest : ? – Niel de Beaudrap Feb 25 '14 at 6:14