Ein Sof

Ein Sof, also known as the Realm of Everything and Nothing and the Paradoxical Space, is the divine and most ancient realm that exists outside of all Creation, encompassing it in its totality.

It is beyond the Four Worlds and is the halo of the Adam Kadmon.

Summary
Ein Sof is the divine and primordial that was formed when the Archangels were created as their brilliant accidentally gave birth to it. However, it neither is nor isn't an Olam (עוֹלָם‎; "World" or "Eon") as such a term cannot be applied to the Ein Sof.

In this realm, duality, space, time, infinite, finite, life, death, existence, and nonexistence are absolutely meaningless, nullified by the very presence of God and can only be a maybe as dictated by the Archangels themselves. It is referred to as "The Outside" or "The Realm of Everything and Nothing" as it is a realm where the concept of Nothingness is made manifest.

It is a place beyond time, space, void, fate, and death, freed from all restrictions and constraints that are within even the core essence of Adam Kadmon. It is the background collective unity that lies beyond Creation which is merely a mere infinitesimal blip within its entirety.

Despite its titles, it cannot be described as the highest form because the realm exists beyond definition.

Quotes
"Any name of God which is found in the Bible can not be applied to the Deity prior to His self-manifestation in the Creation, because the letters of those names were produced only after the emanation... Moreover, a name implies a limitation in its bearer; and this is impossible in connection with the "Ein Sof"."

- Minḥat Yehudah

"Before He gave any shape to the world, before He produced any form, He was alone, without form and without resemblance to anything else. Who then can comprehend how He was before the Creation? Hence it is forbidden to lend Him any form or similitude, or even to call Him by His sacred name, or to indicate Him by a single letter or a single point... But after He created the form of the Heavenly Man, He used him as a chariot wherein to descend, and He wishes to be called after His form, which is the sacred name "YHWH""

- Zohar

Trivia

 * According to Azazel, Ein Sof could be likened to the library of which the shelves of Adam Kadmon are contained.
 * Ein Sof in Kabbalah is the state God was in prior to self-manifestation. The term was first used by Azriel of Gerona, one of the most important Kabbalists at that time, who held Neoplatonic beliefs and thought that God can have no thought, no desire, or action as all of these are negated by it. It is the origin of the Ohr Ein Sof (The Divine Infinite Light).
 * In Lurianic Kabbalah, the Tzimtzum (Self-Withdrawal), which is the first act of Creation, takes place within the Ein Sof to create an empty void from which all of Creation springs from.
 * Ein Sof springs from the concept of Ayin, which is the Nonexistence beyond Nonexistence and Existence and cannot be defined. In the Tzimtzum's order of de-evolution into our physical creation, Ein Sof is defined as 00.