Changes the current selection to any polygon faces associated with the components that were originally selected.
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 Faces, any faces that are associated with the selected vertices are selected. That is, the four faces that are connected to a vertex get selected for each vertex that was 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.