Changes the current polygon selection to any polygon edges that are associated with the selected polygon components.
For example, if you have a polygon mesh comprised of four-sided polygons (quads) with several vertices selected and then choose Select > Convert Selection > To Edges, any edges that are associated with the selected vertices are selected. That is, the four edges that are connected to each vertex get selected.
Many of the convert selection features are available from the context sensitive polygon marking menu when you press 
+ 
whenever a polygon component is selected.