A puzzle in which you need to find and follow links to successive i.stack.imgur images in order to progress.
What is imgur?
Imgur is the website which hosts images on SE. The website dedicated to images is i.stack.imgur.com.
How do I find the next image?
Images on SE will have a 5 symbol code. For instance the image below:
has the code 'z4TVQ'. Its URL is i.stack.imgur.com/z4TVQ.png.
So if you are solving or making a puzzle, you should look for a 5 symbol phrase, an eight symbol phrase that ends in an image file format, or an encoding of a complete URL in that format.