Wabi-sabi represents a comprehensive Japanese world view or aesthetic. It is difficult to explain wabi-sabi in Western terms, but the aesthetic is sometimes described as one of beauty that is imperfect, impermanent, or incomplete.
Wabi-sabi is the quintessential Japanese aesthetic. It is a beauty of things imperfect, impermanent, and incomplete. It is a beauty of things modest and humble. It is a beauty of things unconventional...
It is also two separate words, with related but different meanings. "Wabi" is the kind of perfect beauty that is seemingly-paradoxically caused by just the right kind of imperfection, such as an asymmetry in a ceramic bowl which reflects the handmade craftsmanship, as opposed to another bowl which is perfect, but soul-less and machine-made.
"Sabi" is the kind of beauty that can come only with age, such as the patina on a very old bronze statue.