“Mono no aware” (もののあはれ), almost certainly some essence lost in translation, is Japanese for “the pathos of things”, “an empathy towards things”, or “sensitivity to ephemera”. 

More sentiment than term, it adds flavour from Japan to the philosophy of “impermanence”, with emphasis on flavour, just like a well known biting of apples koan.   

“Mono no aware” is more than concept or mental construction. It is the everyday awareness and experience of things to be fleeting, and the gentle feeling — sadness — with even deeper sadness beneath, reminder of transience as the true nature of life.