A kōan, “public case”, is an episode or saying of a past master, such as Zhaozhou’s answer “Mu” to whether a dog has buddha-nature. In Rinzai Zen the student works with kōans under a teacher, exhausting conceptual thought until insight breaks through. Collections include the Gateless Gate and the Blue Cliff Record.
Kōan
A case from the Chan or Zen tradition, often a paradoxical exchange, used to provoke awakening.
Also: Koan, gong’an