Japanese 悟り, a Buddhist term for the experience of reality, the voidness or emptiness (shunyata). Comparable to the Sanskrit word samadhi.
"Zen only begins at the moment when one first attains Satori; before that one merely stands outside and looks at Zen intellectually. In a deeper sense, Satori is only the beginning, but is not the end of Zen..." —G.C.C.Chang, The Practice of Zen (1959)
"The so-called [spiritual] practice or work is merely a method for purifying the shadows of our habitual thinking and flowing thoughts. To concentrate all one’s efforts to this end is called “work." If suddenly the surging thoughts stop, one clearly sees that his selfmind is originally pure, genuine, vast, illuminating, perfect, and devoid of objects. This is called “Wu" (Japanese: Satori). There is nothing outside of the mind, nothing which can be worked upon, and nothing to be enlightened... However, the egotistic passions, long accumulated and rooted within us, are difficult to wipe out." —Master Han Shan, quoted by G.C.C.Chang, The Practice of Zen (1959)