Subpages can be hidden from the published and preview versions of your site, through the editor. Do take note, you cannot link to any hidden subpages or any of its content.
To hide a subpage:
1. In the left editing panel of the site editor, hover over the subpage you want to hide and click on Edit.
2. Tick the box for Hide subpage.
3. Click Save.
Note: You'll now see the icon below if a subpage is hidden. To unhide, just go through the same process and un-check the box then save.