Ensō (circle) is a sacred symbol in the Zen school of Buddhism
"form is void and void is form"
The ancient ensō symbol refers to the beginning and end of all things, the circle of life and the connectedness of existence. It can symbolize emptiness or fullness, presence or absence. All things might be contained within, or, conversely, excluded by its boundaries. It can symbolize infinity, the “no-thing”, the perfect meditative state, and Satori or enlightenment.