Here is a short video showing how to hide and show a page (same applies to folders):
How to hide a page or folder:
Open the Action menu > Edit menu > Drag the page from the menu below to the field with the text "Drag pages or folders here to hide them from menu.".
This will hide the page or folder from the menu, but will not delete it.
The page can be accessed by administrators from Menu > List all pages at any given time.
Participants can also access the page, if some notification email leads them there (handy, if you'd like them to give feedback, but not be able to see the page again later - send them an invite to that page, but never drag it to the menu).
This is also convenient for administrators, because they can work on certain pages without putting them visible, and once the page is ready for the participants, it can be revealed.
How to show the page or folder in the menu:
Open the Action menu > Edit menu > Drag the page or folder back to the menu and place it in whichever order you'd like and it is again available.