guest pass

 guest pass  is a feature of at least one silo (Flickr) that allows a user to create a special URL to an otherwise private/protected post or collection, that the user can send that URL to others (like over email or chat), where viewing it would set a cookie and redirect them to the actual protected content URL, allowing them to browse it without signing in or otherwise creating a silo account, and (used to) display a prominent banner that they were viewing that content via a Guest Pass.

vs capability URL
A guest pass is different from a capability URL, in that the guest pass encodes some form of elevated access-state which persists in the viewer's browser (typically via cookies), so they can return via an otherwise normal permalink URL. That elevated access-state is typically displayed to the viewer in the form of a banner usually above the content, clearly communicating that the viewer is seeing something that is not otherwise publicly accessible.

Flickr
See:
 * https://help.flickr.com/en_us/create-or-delete-temporary-guest-passes-in-flickr-Bygpmj1Q