Advaita is difficult to discuss; ajata is infinitely more so. 

Advaita tells us that reality is “not two”. Ajata tells us that it is “not even one". 

Ajata translates as “no creation”. This means to say that nowhere has anything ever come into being. Therefore, the entire universe (or universes) — and everything therein — has no reality. In other words, the ultimate condition is nothing, or nothingness. 

Advaita is to ajata, as milk is to cream. In Advaita, we come to realize that “all that is, is That,” or the Absolute. Ajata is where we subsequently come to realize that there is not even That (or the Absolute).

Technically, from the standpoint of ajata, even nothingness is non-existent. 

In the attempt to “explain” nothingness, consider that the point of view is meant to be through your eyes; if it is to be understood, it is you for whom the comprehension matters.

The first part of the comprehension is to recognize that when you draw your last breath, you will no longer know that you had ever lived, 

Not knowing that you had ever lived, you would not have ever known that there was even a universe (or anything “in” it). This includes any other “people” or consciousnesses. 

You will not have known or had awareness that anything ever had “existence” or “nonexistence”. 

The second part of this comprehension of ajata is that you definitely will draw your last breath. 

We cannot even say that the existence of you, or anything else, has been so much as a dream, because “existence” or “nonexistence” are merely classifications within the “dream”. 

It will come to be, in fact, that everything — which could possibly claim that it was existent — will not even know that it (or anything else) had ever existed. 

When you can come to recognize that this (ajata) is true for you, you can recognize that it is true for everyone, every “you”, everything which is said to exist. 

So, the point of ajata is that not anything is ever actually real — even categories of “existent” or “nonexistent”. 

You will not even be aware of “nothingness” ultimately, so we cannot even call emptiness by any names (not even the Absolute). 

And it is to that “void” to which ajata is pointing. 

It is no wonder that it is only someone who is thoroughly conversant with advaita who can come to “understand” ajata (or “nothingness”). 

This nothing means not anything has ever ultimately existed as real. (Not even “nothingness”.) 

From Wikipedia, at “Ajativada” (the teachings of ajata): In the Vedic Nasadiya Sukta 10:129, the first line reflects Ajativada: “Then even nothingness was not, nor existence” circa 10,000 BCE