The lower-case letter μ is used as a symbol for:
Mu is the name of a (hypothetical) vanished continent, located in the Pacific Ocean but now, like Atlantis and Lemuria, sunk beneath the waters. The idea of this continent first appeared in the works of the antiquitarian Augustus Le Plongeon (1826-1908), a 19th century traveler and writer who conducted his own investigations of the Maya ruins in Yucatán. He announced that he had translated the ancient Mayan writings, which supposedly showed that the Maya of Yucatán were older than the later civilizations of Atlantis and Egypt, and additionally told the story of an even older continent of Mu, which had foundered in a similar fashion to Atlantis, with the survivors founding the Maya civilisation. (Later students of the Ancient Maya writings believe that Le Plongeon's "translations" were based on little more than his vivid imagination. )
This lost continent was later popularised by James Churchward in a series of books, beginning with 'Lost Continent of Mu' (1926). The books still have devotees, but they are not considered serious archaeology, and nowadays are found in bookshops classed under `New Age' or `Religion and Spirituality'
Geologists maintain that we may be quite certain that no such Pacific continent existed. Continental masses are composed of the lighter "sial" (silicon/aluminum) type rocks which literally float on the heavier "sima" (silicon/magnesium) rocks which constitute ocean bottoms. The Pacific basin is noticeably lacking in sial rock. (See plate tectonics)
Mu (無) is a Japanese word meaning "null", "nothing", "emptiness", "vacuum", "void". It is used as a response to certain koans and other philosophical questions in Zen Buddhism, with the meaning, "Your question is inherently nonsensical and irrelevant."
Some earlier thinkers had maintained that creatures such as dogs did have the Buddha nature; others, that they did not. Joshu sought to avoid this speculation by pointing out that it was a waste of time.
See also: two-letter English word