(1) The absolute void, complete vacuity, said to be the nirvana of the Hīnayāna. (2) The essence of thebhūtatathatā, as the 空真如 of the 起信論, 唯識, and 華嚴. (3) The void or immaterial as reality, as essential or substantial, the 非空之空 not-void void, the ultimate reality, the highest Mahāyāna concept of true voidness, or of ultimate reality.