Iyun (deep study into something) is when a person goes over the conceived thing and looks into it very much which is the slowing down -the opposite of going over a subject fast- that is, in order to come to the depths of the concept as it is in its essential self innerness and the inner insides of it specifically.
At first glance this Iyun is what is called the deep concentration of the mind in the language of the world, but it is not so since the concentration of the mind is just a vessel to come to the depths of the thing actually (as it is). That is, the contemplative or meditative concentration is only a vessel to get to the depth of a subject. Whereas the Iyun of Binah, that is, intensive analytical explanatory study is the vessel to the actual subject itself.
And Now Chapter 1.09
Now, in addition to the level of the depth of Binah (Understanding), which is reached by the process of Eeyun, there is also a way to reach up into the depth of the Chochmah (Wisdom) itself. To reach higher than this depth of Binah through an even deeper concentration, is what is called Ma’amik (deep delving). This process of Ma’amik reaches higher than even the Chochmah itself. Even though Chochmah is the total Ein - ‘nothingness’ - of an idea (meaning the completely abstract and unexplainable perception of the mind's eye) before it comes within the reaches of the depth of the point of the understanding (musag) of Binah , like a wellspring to a river, as mentioned previously. A wellspring serves as the source to the river and there is a perceptible connection between them. This, however, is only as the water surfaces. On the other hand, when the water is still contained within the depth of the ground it can not yet be recognized as a source for a river, for this can only happen once it goes up from its source to spill over on dry land.
So too, the inner depth of Chochmah is not yet connected to the understanding of Binah, for it is still more quintessential than the explanation. It is only the extension of the Chochmah where it surfaces in the consciousness and can ‘spill over’ into the understanding of Binah.
However, delving deeply into the source of an idea reaches up into the inner source which causes the outpouring of the wellspring of Chochmah etc., and this inner source of the revealed flow of thought is called the depth of Chochmah or the hidden Chochmah.