A 'ghost page' is a page that the wiki generates as a temporary reference or preview page that is shaded in gray. This ghost page can be used to compare earlier version of a page or, as we learn more about the wiki, as a page that is the result of some form of analysis on the wiki.
This temporary page is valuable if you would like to revert your page back to an earlier version. To do that, simply click on the fork symbol next to the "+" symbol on the lower right corner of the journal.
helpful trick
If you would like to delete a page in your wiki, click on the very first icon in the journal, the sun. This click will bring up the ghost page at views it when it was first created. By then clicking the fork icon on this ghost page you will revert back to the pre-created state, removing the page from your wiki.
example