Active Points vs Selected Points»
Active points are those that you can see, and move with the mouse when the Contour tool is selected:
When View > Show > Nodes is on, all nodes in the current element are active. When Edit > Edit Across Elements is on as well, all nodes in all elements of the current glyph are active. When Edit > Edit Across Glyphs is on too, all nodes in all elements of all glyphs are active.
Inactive points are those that are not shown, or are displayed as tiny and black (depending on Preferences > Glyph Window > Inactive nodes), and cannot be moved with the Contour tool:
Selected points are those that are currently selected. They are shown in red: