Daath, Hebrew, “knowledge,” is the non-Sephirah in the midst of the Abyss, situated on the Middle Pillar of the Kabbalah Tree of Life between Kether and Tiphareth. Daath in many ways is the most controversial element of the Kabbalistic tree, being both complex and obscure. It is a downward reflection of Kether, representing the closest thing to the knowledge of Kether that is attainable below the Abyss. It is also knowledge, in the Biblical sense, of Chokmah and Binah, the primal male and female centers of the tree.
Standard symbolism:
Astrological Correspondence: Sirius, the Dog Star
Tarot Correspondence: The triumps as a whole
Elemental Correspondence: Air
Magical Image: A head with two faces
Additional Symbol: The empty room; the pyramid; the absence of all symbolism
Colors:
in Atziluth – lavendar,
in Briah – pale silver-gtay,
in Yetzirah – pure violet,
in Assiah – gray flecked with gold
Correspondence in the Microcosm: The conjunction of Ruach (the conscious self) and neshamah (the higher spiritual self)
Correspondence in the Body: The neck
Daath refers to, or is, the omnipresence knowledge of God throughout the Sephiroth, not just in one Sephirah. This is why Daath means knowledge. Daath includes the first conscious knowledge, hokhmah, of Kether down to the last distinct and created reflection of the Sephiroth. In Binah Daath is not longer hokhmah, pure contemplation, but becomes accessible; in Binah, ontocosmological intelligence becomes the common intellection of the seven lower Sephirahs by which universal creation is conceived, constructed, and ruled. Even though Daath appears vaguely in the Kabbalistic tree it is not a Sephirah, or the eleventh Sephirah of the Sephiroth; ten Sephirahs complete the Sephiroth and Daath is the knowledge throughout. A.G.H.
Sources:
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul, MN, Llewellyn Worldwide. pp. 123
Schaya, Leo, The Universal Meaning of the Kabbalah, Secaucus, NJ, University Books. 1971. p. 32-33