온갖 물체를 여의고 아무 것도 없는 곳. 곧 공계 (空界). 그러나 허공 (虛空)과 공계 (空界)의 다른 점은, 허공이 비색 (非色), 무견 (無見), 무대 (無對), 무루 (無漏), 무위 (無爲)임에 대해, 공계 (空界)는 시색 (是色), 유견 (有見), 유대 (有對), 유루 (有漏), 유위 (有爲)라는 것

Empty space: Space as a non-created element which embraces everything in itself and hinders nothing. A sphere of emptiness where there are no material qualities or elements. Yet the difference between "empty space 虛空" and "empty sphere 空界" is that in "empty space," there is no material elements, no conceptions or ideas, no comparisons; it is undefiled, pure, and non-doing. "Empty sphere" is the world of form or mark, conception and mental activity, comparison, defilement, and phenomena and conditioned.