A kōan (公案?) /ˈkoʊ.ɑːn/; Chinese: 公案; pinyin: gōng'àn; Korean: 공안 (kong'an); Vietnamese: công án) is a story, dialogue, question, or statement, which is used in Zen-practice to provoke the "great doubt", and test a student's progress in Zen practice.
Read more about Kōan: Etymology, Doctrinal Background, Koan-practice, Classical Kōan Collections