Google Wonder Wheel isaa feature of Google Search which shows related search terms to the current searched query in a pictorial format, just like a wheel. This gives you more options to gain more information.
To access the Wonder Wheel, visit Google.com and enter your search term. I entered “Windows Tweaker”. Now in the right panel, expand the “More” and click on Wonder Wheel.
The term Windows Tweaker results are now displayed along with a sort of a wheel which also highlights related search terms.
Click on any of the related links and you will see a new Wonder Wheel generated, which is connected to the original wheel.
Google Wonder Wheel can also be used as a keyword research tool and a great idea generator, if you are looking for something to write on about a particular topic!
UPDATE: They seem to have discontinued it now. Go see some Google Search Fun Tricks instead.