The Upanishads (उपनिषद्) are Hindu scriptures that constitute the core teachings of Vedanta.They are latter part of the four Vedas and are also known as Jnana Kanda (The Knowledge Part). Shankaracharya defines Upanishads as "knowledge of the Self or Brahman (ब्रह्मविद्या / आत्मविद्या) which removes ignorance about the Self". Other dictionary meanings include "esoteric doctrine" and "secret doctrine".
Shankaracharya has composed commentaries on eleven mukhya or principal Upanishads, those that are generally regarded as the oldest. The list of 108 canonical Upanishads is found in Muktikopanishad.