Wabi-Sabi & Zen
The influence of Zen Buddhism makes defining Japanese philosophical terms difficult. Zen Buddhism focuses on doing rather than thinking - enlightenment is not a product of Socratic discourse. Whether it is meditation, chores, calligraphy, the aim is to leave behind the duality which seems inherent to the world.
For all of the aesthetic terms we come across it is useful to try and come at them from different perspectives and to try and hold the basic principles in mind rather than a strict definition.
However, Zen Buddhism was not the source of these ideas, they were developing well before its arrival in the 12th Century. Zen thrived in Japan because it fit so well with an existing aesthetic, ethical and metaphysical framework.
Donald Keene argued that it was the feminine literature of early Japan which drove the development of this worldview. And we only have to look to the Japanese masterpiece of the 11th Century The Tale of the Genji by Murasaki Shikibu to find:
“You that in far-off countries of the sky can dwell secure, look back upon me here; for I am weary of this frail world's decay.”