magic circle

/M AE1 JH IH0 K S ER0 K AH0 L/
noun
  1. 1

    (magic) A circle marked by a practitioner of magic, used as magical protection or to form a magical area.

  2. 2

    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.

  3. 3

    The imagined boundary that separates the player's immersion in virtual reality from the real world.

Source: https://en.wiktionary.org/wiki/magic%20circle