(literary) the illusory nature of life; a profound realization of the world's vanity. Derived from the philosopher 庄子 zhuāng​zi who described the human experience as a great dream from which one must eventually wake up.

the state of being under an illusion or stubbornly refusing to wake up to reality (often used in the phrase 大梦初醒 dà​mèng​chū​xǐng)