The Upanishads are a collection of texts which
contain utterances (Sruti) concerning the nature
of Ultimate Reality (Brahman) and describing
the character of and path to human salvation
(Moksha or Mukti).
They are called Vedanta, the “last chapters
of the Vedas”. The concepts of Ultimate Reality
(Brahman) and the Soul or Self (Atman)
are central ideas in all the Upanishads.
“Know your Ātman” is their thematic focus.
More than 200 Upanishads are known, of which
the first dozen or so are the oldest and most
important and are referred to as the principal
or main (mukhya) Upanishads.