Hard to explain, really.
Wabi-Sabi is a Japanese term, obviously. It's been semi-mainstreamed by the American gardening and decorating industry.
In a nutshell it means - an appreciation for that which is not perfect.
Finding beauty in something old and rusty is wabi-sabi. Picking something up off the side of the road and using it in a new way is wabi-sabi. Making do with what you have is wabi-sabi.
It's a lovely concept that describes us, our house, our yard, and our magical life together - appreciated, loved and perfect in our own imperfect way.