Wabi means things that are fresh and simple. It denotes simplicity and quietude, and also incorporates rustic beauty. It includs both that which is made by nature, and that which is made by man. It also can mean an accidental or happenstance element (or perhaps even a small flaw) which gives elegance and uniqueness to the whole, such as the pattern made by a flowing glaze on a piece of ceramics.
Sabi means things whose beauty stems from age. It refers to the patina of age, the concept that changes due to use may make an object more beautiful and valuable. This also incorporates an appreciation of the cycles of life and careful, artful mending of damage.
"Wabi is the quality of a rustic, yet refined, solitary beauty. Sabi is that trait, be it the green corrosion of bronze, or the pattern of moss and lichen on wood and stone, that comes with weathering and age."