I have on one occasion before this, tried to describe to a co-worker of mine an answer (In my words) to the very question you have posed. Very shortly into my telling her some of the following ideas, and being the extreme religious type that she is, she told me it was Jesus. Be that as it may, it did not appear to me she was trying to understand what I was telling her so, likewise, I did not entertain the idea.
It is almost indescribable. I can not tell you what it literally is, or how people generally perceive it, but I can tell you what/where I know it to be. Right now in this realm, it is only a place in the mind, but can stimulate the senses, allowing you to actually feel it. Have you ever really envisioned yourself in a place (maybe you are not even there, but you can see it) where you are surrounded by objects (possibly people) that are linked to your deepest emotions and desires? Or maybe you had a dream, and when you awoke, it affected your day such that you contemplated giving up the life you know and living in that dream. It is a place outside of the physical realm (or reality as we know it), where everything around you is a representation of your emotions/desires, or in other words, absolute perfection. It is utopia. I believe this is the highest achievement for a human being. I personally spend a significant amount of time imagining myself in a place like this, and even though I can only imagine it, I can actually feel it, usually for very short periods of time. The closest thing to Ethereal, in regards to what can be studied, is heaven. If I had the ability I would not hesitate to enter into this realm and never return.