In Michael’s screenshots, it looks like vertices can be regarded as loose. However, I can only get edges selected as loose elements.
Here, I’m in Edit Mode with Edge Select switched on.
Select>Select by trail>Loose Geometry
results in the selection of an edge.
However, changing to vertex select and doing the same thing
results in nothing being selected.
I was expecting the vertex at the end of the loose edge to get selected.
Can vertices be ‘loose’?