noun

• (Zen Buddhism) A story about a Zen master and his student, sometimes like a riddle, other times like a fable, which has become an object of Zen study, and which, when meditated upon, may unlock mechanisms in the Zen student’s mind leading to satori.
• A riddle with no solution, used to provoke reflection on the inadequacy of logical reasoning, and to lead to enlightenment.
• A therapy technique used by Traditional Chinese medicinal physicians or medical practitioners to break a presenting patients habitual pattern of thinking that has been diagnosed as the primary cause of a illness or disease.