The Upanishads are late Vedic Sanskrit texts of religious teaching and ideas still revered in Hinduism. Of all Vedic literature, the Upanishads alone are widely known, and their central ideas are at the spiritual core of Hinduism. Around 108 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 Upanishads. The Katha Upanishad is the legendary story of a little boy, Nachiketa - the son of Sage Vajasravasa, who meets Yama (the Hindu deity of death). Their conversation evolves to a discussion of the nature of man, knowledge, Atman (Soul, Self) and moksha (liberation).