From the Wikipedia article on Japanese Aesthetics:
Yūgen (幽玄) is an important concept in traditional Japanese aesthetics. The exact translation of the word depends on the context. In the Chinese philosophical texts the term was taken from, yūgen meant “dim”, “deep” or “mysterious”. In the criticism of Japanese waka poetry, it was used to describe the subtle profundity of things that are only vaguely suggested by the poems.
Yūgen is said to mean “a profound, mysterious sense of the beauty of the universe… and the sad beauty of human suffering”.
Yūgen suggests that beyond what can be said but is not an allusion to another world. It is about this world, this experience.
(Ortolani, 325). Ortolani, Benito. The Japanese Theatre. Princeton University Press: Princeton, 1995
When I wake up early enough to see the sunrise, if I keep still and watch for a few minutes I can actually perceive the movement. At these times I become vibrantly aware that I am here, standing at this particular spot on the surface of this particular world; and this world is turning, turning, turning this part of its face toward the star we call the sun, 93 million miles away. And half of this world is at this moment experiencing this very same sun along with me, while the other half is in darkness.
These are my moments of yūgen.