The Upaniṣads are the last part of the Vedic literature, composed over several centuries from around the seventh century BCE. In dialogues, stories and riddles they turn from ritual to the inner meaning of things: the self, Brahman, and the knowledge that liberates. About a dozen are counted as principal, among them the Bṛhadāraṇyaka, Chāndogya, Kaṭha and Māṇḍūkya. They are the foundation of Vedānta.
Upaniṣad
One of the philosophical texts that close the Vedas, teaching the identity of the self and Brahman.
Also: Upanishad, Upanishads