The meaning of upanishad is “to sit near attentively.” They usually consisted of a metaphysical discussion between the sage and a disciple. There are 108 Upanishads traditionally, although only a dozen, the so-called major Upanishads, are in every list.
Minor Upanishads are still being written. In the early Vedic period, before the Upanishads were recognized as authoritative, there was a three-fold division of the Vedas: the Samhita (collection of hymns), Brâhmanas (commentaries), and Âranyakas (forest texts).
The Upanishads formed the last (anta) part of the Vedas, also called Vedânta (from veda and anta). The Vedas were the earliest Indian scripture and have always had the greatest authority. However, that does not mean that if a story or a figure is not mentioned in the Vedas, it is considered untrue or without authority.
In fact, there were a number of ways of resolving such a problem. First, it could be said to be additional revelation and therefore compatible. Or, it could be new (that is, not mentioned in the Vedas) and a necessary supplement, given the declining spirituality of each of the four yugas.
New revelations were needed for the kali yuga, the one we are in now. Many more ways were available to allow for discrepancies and even contradictions to the Vedas in later Purânic and Tântric mythology. One major Upanishad, the Isha, presented a woman sage teaching the devas (gods) about the Absolute (Brahman).
Some of the important Upanishads are the Taittirîya Upanishad, Mândukya Upanishad, and the Brihadâranyaka Upanishad. The Brihadâranyaka Upanishad is the longest Upanishad. The Upanishads are known as one of the foundational pillars (prasthânatreya, “three pillars”) of Indian thought.
Because of their deeply philosophical and meditational approach, the Upanishads provide few myths—and only several names of sages with some ideals like union (samadhi) with the Absolute (Brahman).