The phrase is a common search string used by people trying to find open web directories. These "indexes" are essentially folders on a server that haven't been properly secured, leaving their contents—often photos and documents—visible to anyone with the link.
Search engines crawl these pages just like any other website. If a folder isn't explicitly told not to be indexed via a robots.txt file or server settings, it becomes searchable by the entire world. The Risks of Accessing and Hosting For the Viewer: parent directory index of private images free
If your directory goes viral, the sudden influx of traffic can crash your hosting or lead to massive overage fees. How to Prevent Your Images from Being Indexed The phrase is a common search string used
Accessing data that was clearly intended to be private can fall into a legal gray area depending on your jurisdiction. Ethically, viewing or distributing someone’s personal "private images" is a major violation of privacy. For the Owner: If a folder isn't explicitly told not to