a circle of mushrooms often seen on grassy ground, originating from one initial mycelium and often accompanied by a circle of darker grass: so called because formerly thought to have been made by the dancing of fairies
See fairy ring in American Heritage Dictionary 4
noun
A circle of mushrooms in a grassy area, marking the periphery of perennial underground mycelial growth.
Origin:
Origin: From the belief that it is a dancing place for fairies