2. A Chinese word for "nothing". According to some (such as the Discordians and Douglas Hofstadter), it is also a Japanese word alleged to mean "Your question cannot be answered because it depends on incorrect assumptions", as in the anecdote: "A monk asked Joshu, 'Does a dog have the Buddha nature?' Joshu retorted, 'Mu!'" Some sentients jokingly argue that any Turing test can be passed if the subject simply answers "Mu" to all questions.
3. See: Om.