What is a flickr guest pass?

Most of my pictures on the photo platform flickr are public, i.e. visible for everyone. However, I have marked some pictures that I am not allowed or do not want to show publicly as „private“. Via a special link („guest pass“) I give selected addressees access to the private photos of my albums. After a few weeks I deactivate the guest pass in order to keep the overview; thereafter the link no longer works. However, the public photos will permanently remain accessible via my homepage or my flickr page.