Wabi-sabi (侘寂) is way of viewing a world centered on the acceptance of imperfection and transience.
It is one of Japanese traditional aesthetics.
The words Wabi and Sabi were originally used separately, but they are usually combined together as one expression in these modern days.
The meaning of Wabi and Sabi are explained individually as follows:
Wabi（侘、侘び) is an attitude to find out a feeling of fullness in lack, insufficiency, imperfect and incomplete.
Wabi is the noun form of the verb “Wabu” which means “desolateness”, “comfortless”, “lonesome” and “winterly”.
The original meaning of Wabi is a feeling of dislike, however, as one goes forward in time, it was changed to aesthetics which phrase the attitude of seeking beauty and inner contentment in simplicity and imperfection.
Wabi is thought to have developed rapidly alongside the spirit of the tea ceremony during the Muromachi Period (1336-1573) and then, matured in Edo Period (1603-1868).
The reason of why the acceptance of imperfection is considered meaningful, because imperfection is everywhere.
And therefore, “acceptance” is the key for living.
In Japan, there is another concept which is that “something perfect is not good at all”.
And therefore, even when making the imperial palace, one place is always left unbuild according to Tsurezuregusa (a collection of Japanese essays) written in the Kamakura period.
Another example is that leaving three piece of tiles on the roof in Edo Period.
Because after completion of framework, it denotes the start of ruin or destruction of a building.
Therefore, carpenter in Edo Period left three piece of tiles on the roof on purpose and it is intended to protsect living place by the action of making something look as if it is unfinished.
A further example is an inverted pillar in Nikkō Tōshō-gū (日光東照宮).
The act of inverting one pillar out of twelve pillars is erected to ward off evil spirits, because of perfect to be possessed by an evil spirit.
If you visit Nikkō Tōshō-gū, you can identify that only one of its pillars was erected upside-down, because it has carving patters upside-down.
Considering the above, the concept of Wabi seems to be commonly used in Japanese culture since ancient times.
Sabi is the attitude of seeking beauty in withered things where their internal essence is oozing out to the surface, an example of which is a stone covered with moss.
In this case, the moss is the attribute of the richness.
Sabi is the noun form of the verb “Sabu” which means “declining”, “deserted”, “lonesome” and “rusting”.
Sabi is beauty of the state of being profound and fertility which is exuded spontaneously in strained quiet loneliness and silence.
So, old dried-up and rich elegance which are basically contrary to each other are interplayed and activated inside the boundary.
This directly-opposed ideas and the beauty of double structure is considered Sabi.
Finding beauty in old material is similar to antique, however, antique has a tendency on historical meanings but Sabi is more focused on natural process.