Kadmon

The name Kadmon refers to the essence of the Holy One, Blessed be He. Unlike the title "Ohr Ein Sof" which means "Light that is Infinite" rather than "Light of the Infinite One," His blessed essence is an existence that has no beginning, which is a greater quality than the attribute of being infinite. This is as written by the Rama: "For every Kadmon is eternal, but not every eternal thing is Kadmon, as many created beings will be eternal by the Creator's will." This is also mentioned in the Rambam's Guide for the Perplexed regarding the existence of the sun and moon, as there are verses which indicate they exist forever, as it is written: "He established them forever and ever; He made a decree which shall not pass away."

The meaning of this is that every "Kadmon" - namely, an essential existence that was not preceded by a state of non-existence, but was and always is, because its existence is true-existence from itself - must necessarily also be eternal, because true existence never ceases to exist.

But an existence that is merely eternal - meaning it never ceases to exist - is not necessarily also "Kadmon," because it is possible that although it is not true-existence, and its existence was preceded by a state of non-existence, nevertheless it is eternal in the sense that it never ceases to exist.

This is because this eternality it possesses does not come from its own power but stems from Hashem's will that maintains it continuously.

Tzachtzachot

Tzachtzachot is the first root of the Sefirot, as they "exist" in Atik Yomin or in Akudim. At this level, the Sefirot are not arranged in three lines (right, left, and center), or even in two (right and left), but are included in a single point: in Atik in a manner of "there is no left in this Ancient One," and in Akudim in a manner of "bound in one vessel."