Being part of Google Labs means it is still in the development stage, but works.
Image swirl is a visual way to search for images and it shows their relationships to other images in groups.
Enter your search term and click enter and you get a screen like the one below (I searched "Physics").
As you can see, each image has a stack behind it. Click on an image and it brings up a circle of images. Click on another image in there, and it brings up another circle with that image and more that are related.
I like it because it is more visual than the basic image search and you can find related images much easier. It is great for helping students find images that are connected and exploring those connections.