Other forms: koans
In Zen Buddhism, a koan is a surprising and often perplexing phrase that's used as a meditation tool. A well-known koan is "What is the sound of one hand clapping?"
It's common in Zen Buddhist training for a teacher to present a koan to a student, often in the form of a question. Because of their paradoxical nature, koans are nearly impossible to answer, and students are expected to "sit with" them while meditating. Ideally, the koan eventually leads to enlightenment — and at the very least, it challenges the mind. The Japanese koān means "public matter for thought."