Wiktionary
mono no aware
n. A wistful awareness of the impermanence or transience of things.
Wikipedia
Mono no aware
, literally "the pathos of things", and also translated as "an empathy toward things", or "a sensitivity to ephemera", is a Japanese term for the awareness of , or transience of things, and both a transient gentle sadness (or wistfulness) at their passing as well as a longer, deeper gentle sadness about this state being the reality of life.
Usage examples of "mono no aware".
He watched the snowflakes fall as he listened to the music, and he was filled with mono no aware for the transience of beauty in the world.