crop circle 
noun
An area of standing crops which has been flattened in the form of a circle or more complex pattern. No general cause of crop circles has been identified although various natural and unorthodox explanations have been put forward; many are known to have been hoaxes.A farmer claims to have witnessed the formation of a crop circle in a barley field....
- A crop circle in Ontario this year attracted more than 5,000 people to the site.
- I was taking a group of crop circle enthusiasts from London on a crop circle visit and this was the event I had chosen.