Upanishad refers to a type of scripture in
Hinduism, the name is derived from the
Sanskrit words upa (near), ni (down) and s(h)ad (to sit) i.e. sitting down near. The term implies listening closely to the secret doctrines of a spiritual teacher. The oldest and longest of the Upanishads are the
Brihad-Aranyaka[?] and the
Chandogya[?] from about the 7th century B.C. Initially there were over two hundred upanishads but only fifteen were considered important by the philosopher
Shankara[?].