Wabi-cha (わび茶; 侘茶; 侘び茶), is a style of Japanese tea ceremony particularly associated with Sen Rikyū and Takeno Jōō before him. Wabi-cha emphasizes simplicity. The term came into use in the Edo era, prior to which it was known as wabi-suki (侘数寄), suki generally referring to the concept of "artistic inclination," and "wabi" literally meaning 'forlorn'.
There is more detail on the English and Japanese Wikipedia pages.