The Sublime is a concept developed by the German philosopher Immanuel Kant in his Critique of Judgement. It relates a feeling of beauty to abstract mental processes. It has been many years since I have read this rather dry and complicated work myself, so much of this is taken from second hand sources. As in most Kantian works, it requires qite a bit of wading through complicated and seemingly unfeeling terminology to reach a beaitful, universal concept.
According to Kant, the feeling of sublimity rises when there is a gap between what the mind can understand, and what it can represent ot itself. All humans have some sort of concept of peace, and can apply this concept to their daily lives. Sometimes they can even apply this concept in extraordinary circumstances. And from experience with this concept on a practical level, they can imagine total or absolute peace. But what they can't do is represent this concept in their mind, they can not form a picture or diagram or verbal description of it.
This creates what is almost a paradox. On one hand, the concept of say, absolute peace is easy to carry around with us, and is something that we all hope for. And yet not a single person can really visualize or explain what that concept means.
In Kant's view, this is the feeling of The Sublime, a feeling that a picture, a piece of music or a poem hints at a greater truth then it can ever capture in the form it has. I personally believe this idea explains why some art appeals to me, it is the art that I can not explain that always pulls me the most.
And of course, I have to add...What I really want to know I can't define.