When I start Blender, I am shown the Outliner on the right side:
Somehow I very often manage to hide it. I think it happens when I unwrap and have the "UV Edit" window shown on the left side of Blender.
How to restore/show it again?
The shortcut for the outliner window is ShiftF9.
For the shortcuts to other windows see this
When I hide the Outliner by accident, I get it back with Ctrl+Up Arrow. (Ctrl+Down Arrow hides it)
+
and-
on Numpad $\endgroup$