A fairy circle, or ring, is a circle of magic created by or for otherworldly beings. See a previous post to get a brief definition of what a fairy circle, or fairy ring, is if you are not familiar. https://faeriesight.wordpress.com/2010/09/01/fairy-ring/
In various areas along the pro-Namib Desert in Africa, there are mysterious circles that are discs of grass on the ground, which evidently do not grow anything within the ring. You can read a more complete description here.
The original hypothesis was that bugs such as termites were creating these odd, but further studies proved that this may not in fact be the case. They argue that it may be a more ecological, a competition for resources, though that still doesn’t explain the shape. You can read their findings here.
Of course, there are also those who may be more whimsically inclined to theorize that there are more mysterious elements at work here. Maybe a supernatural force, an otherworldly spirit, a portal to another realm. What do you think?