Fairy rings are naturally occurring circles of mushrooms that often appear in grassy areas. They can vary in size and shape, typically forming a ring or arc. These formations are caused by the growth of fungi underground, which spread out in a circular pattern as they seek nutrients. The outer edges of the ring are usually where the mushrooms emerge, while the center may remain bare or have healthier grass. Fairy rings are found worldwide and have been the subject of folklore, but they are primarily a natural phenomenon related to the life cycle of mushrooms.