(Hebrew אצילות; also Atzilut or Olam Atzilut) The First of the Four Worlds of the Kabbalah, whose center of gravity is in the superior triangle of the Tree of Life. This is the World of Archetypes or Emanations, ruled by the sephirah Kether. It is a world of total purity and divinity.
"And a river went out of Eden" (Genesis 2:10) [means] that there are no strange Klipoth ["empty shells" ie. psychological defects, egos] in the Tree of Life above (in Atziluth), as it is written: "For thou art not a God (אל El) that hath pleasure in wickedness: neither shall evil dwell with thee." (Psalm 5:4), but in the tree below (in Briah) does indeed have strange Klipoth." - Zohar
"The highest part of man is the world of intuition and objective spiritual consciousness. In the world of intuition, the archetypes of all things in nature develop." - Samael Aun Weor, The Perfect Matrimony
For a human being to reside in Atziluth, one must be totally clean of sin. This can be reached by completing the second mountain, by which one pays all karma, destroys all inner defects, and dies physically to pay the karma of fornication (eating of the Tree of Knowledge). This is why Jesus, Buddha, and other masters died physically, so they could resurrect and enter the third mountain (which is related to Atziluth) as resurrected masters.