A subtly profound invocation of the imagination.
Japanese: Yūgen (幽玄)
... the Japanese have a word _yugen_, which has no English equivalent whatsoever. Yugen is in a way digging change. It's described poetically, you have the feeling of yugen when you see out in the distant water some ships hidden behind a far-off island. You have the feeling of yugen when you watch wild geese suddenly seen and then lost in the clouds. You have the feeling of yugen when you look across Mt Tamapeis, and you've never been to the other side, and you see the sky beyond. You don't go over there to look and see what's on the other side, that wouldn't be yugen. You let the other side be the other side, and it invokes something in your imagination, but you don't attempt to define it to pin it down. Yugen.
excerpt from The World As Emptiness, by Alan Watts
Yugen avoids the obvious and relates to the subtleties of nature. It is the suggested rather than the totally revealed aspects of it. It involves partly hidden views of indistinct areas sometimes relative to shadows, partial reflections and darkly revealed forms. Yugen hints at extra layers of meaning which are not at first obvious to the casual viewer. It also involves things which are subtlely profound.