magic circle

noun4

1. •
   A circle marked on the ground by a practitioner of magic, used as magical protection or to form a magical area.
2. •
   In traditional cultures, a circle drawn on the ground marking out a sacred, protected, or ritually charged space.

   • On moonlit nights they stood within the Magic Circle and gazed on the glory of the moon, and trembled to the answers that came in the swish of wing as bat-like birds sped by. — 1937
3. •
   The imagined space, separate from the real world, in which players in a virtual reality system experience immersion.
4. •
   An arrangement of natural numbers on circles such that the sum of the numbers on each circle and the sum of numbers on diameter are identical.