A Ghost Page is a page automatically excluded from the Site Tree and the Google Sitemap, not cached by the WP Super Cache plugin and hidden from crawlers without its path showing up in the 'robots.txt' file. Generally a Ghost Page has few to no inbound link. An example of Ghost Page would be the landing page of a successful PayPal transaction, namely an order confirmation page.
To prevent the indexing of a Ghost Page without resorting to a
Disallow rule that might be used by bad-disposed robots to uncover the page, SiteTree sends back an
X-Robots-Tag HTTP header that a trustworthy crawler shouldn't ignore. This is also one of the reasons why the plugin hinder the "supercaching" of such a page.
Flagging a Page as Ghost Page
This can be done by just ticking the 'This is a Ghost Page' checkbox in the editor screen of the page you want cloak and then clicking on the 'Update' button:
Note that neither posts nor custom posts can be flagged as Ghost Pages.