What the Buddhist term empty/emptiness (shunya/shunyata) means depends a lot on the context in which it is used. For example, in the Lankavatara Sutra there are seven different emptinesses.
“Replied Mahamati the Bodhisattva-Mahasattva, I will indeed, Blessed One. The Blessed One said: Emptiness, emptiness, indeed! Mahamati, it is a term whose self-nature is false imagination. Because of one's attachment to false imagination, Mahamati, we have to talk of emptiness, no-birth, non-duality, and absence of self-nature. In short, then, Mahamati, there are seven kinds of emptiness: (1) The emptiness of individual marks (lakshana), (2) the emptiness of self-nature (bhavasvabhava), (3) the emptiness of no-work (apracarita), (4) the emptiness of work (pracarita), (5) the emptiness of all things in the sense that they are unpredicable (nirabhilapya), (6) the emptiness in its highest sense of ultimate reality realisable only by noble wisdom, and (7) the emptiness of mutuality (itaretara) which is the seventh” (trans. D.T. Suzuki).
In the Pali canon, suñña (shunya) can mean lack, vacant, desolate, barren, lonely, absent, etc. The Buddha tells Ananda that the temporal world (loka) is empty (suññam) of what belongs to the self which denotes a lack. The message is, we should not look for our self in the temporal world—it ain’t there.
Also in the Pali canon we find supreme or pure ultimate emptiness, viz., parisuddha paramanuttara suññata described in the discourse, Cula-Suññatâ Sutta, of the Majjhima-Nikaya. This is a state which can only be described as mind that becomes utterly purified, or the same, pure Mind. Mind is able to distinguish its own pristine nature from its most subtle of phenomenalization, namely, animitta-ceto-samadhi ( the samadhi of the mind that is signless). According to this Sutta, animitta-ceto-samadhi is still “effected and thought out” which means it is impermanent and liable to stopping.
Often in Mahayana Buddhism we find emptiness (shunyata) equated with suchness or tathata. Suchness, we are to understand, is the instrinsic substance or nature (svabhava) of Mind which is the Mind that is Bodhi (bodhicitta). In this sense emptiness is ontological or reveals the ontological rather than being the negation of all knowledge claims.
In Zen there is a difference between nihilistic emptiness and pure Mind which is empty of bewitching defilements. From Zen master Tsung-mi we learn:
“Nihilistic emptiness [means] vacuity, openness, absence, or extinction. It does not refer to the Genuine Mind (zhen shi xin). [This kind of emptiness] is without wisdom, without function, and cannot be found within dharmas.”
Again he says,
“The Nirvana Sutra, which says that “when there is nothing in a jar, the jar is said to be empty—it does not mean that there is no jar.” In the same way, “when there are no discriminating thoughts such as desire or anger in the mind, the mind is said to be empty—it does not mean that there is no mind. ‘No mind’ (wu-hsin) only means that the defilements (fan-nao; klesha) have been eliminated from the mind.”
We can consider absolute Mind to be completely empty of any and all determinations—which, in itself, is a sheer, marvelous vacuity which is, nevertheless, real and dynamic. Truth be told, the Buddha taught the emptiness or barrenness of phenomena; that they have no true nature. He also taught the absolute or tathata to be empty of phenomena and determinations.