Literally "Primordial man," the loftiest of the five worlds -- it precedes Atziluth. It occupies an intermediary level between the Infinite Light and the finite creation. "Adam" means "in the likeness of," or "in the image of," from the Hebrew word domeh. "Kadmon" means primordial, or primary. Adam Kadmon is thus the primordial world which is "in the likeness of" the Infinite Light which preceded it and which was concealed in the process of Creation. Thus, even though Adam Kadmon is a world, i.e., it comes into being through the tzimtzum, nevertheless, it is so sublime, pure, and transcendent that it mirrors the Infinite Light. Adam Kadmon is referred to as the "world of keterim" since all of its sefirot are keter-like "meta-sefirot."
Source: Kabbalah On Line
