Allows Administrators to leave notes for themselves and others in Post and Pages.
In Context Admin Notes allows Administrators to leave themselves and other Admins notes inside of posts and pages.
Its primary purpose is for content that is modified on an ongoing basis, or for content that is worked on by different people.
Using a shortcode, you can leave comments for other Admins that will be hidden from normal users.
Of course, this should never, ever be used for any truly sensitive information. As long as the plugin is enabled, and the shortcode used properly, it will work fine, but this is still the point of least security.