Chen,
Very hard question and I will give you sort of a layman's take. This is despite my mother being a Buddhist and my father a Lutheran...and me nothing much.
When I started martial arts and was told to meditate, I could have as easily kept one eye open for all the good it did me. Later, it was outside of martial arts and just trying to accomodate stillness and relaxation. Maybe a beautiful day, maybe just feeling good and sort of letting my mind rest "between the lines" and go outward from there. I mean this literally.
One of the training devices that some Buddhist monks had were to give those nearly nonsensical statements that you tried to wrap your brain around: The sound of one hand clapping, etc. Well, within that verbal and written construct is way to leap off into the deep end of the mind so that you don't have the baggage that your up front, daily brain brings to the game trying to decipher what that means. When considering it or thinking past it---trying to let go, sometimes I have a vague sense of reading some ancient tome and skipping to the blank space between the lines and moving past that...sort of a feeling as my mind does a brain fart and I space out, but a little different since I am actively seeking this sensation.
When that happens if sort of feels like an electric nothing...a skip in the phonograph of my awake mind. I am aware of...nothing... and not trying to be conscious of it. It's a balancing act of trying to get to that point, but not forcing it and allowing it to happen. It is very relaxing when I can do it. And when I come out if, sort of feels like waking up from a nap. I can do this for only a few seconds to less than a minute and only some time.
I don't know if that helps. And to me is probably no different than any self-induced trance like state in countless cultures. I do it to relax.
-B