What is upanishad?

each of a series of Hindu sacred treatises written in Sanskrit c. The Upanishads are late Vedic Sanskrit texts of religious teaching and ideas still revered in Hinduism. The Upanishads (/uːˈpænɪˌʃædz, uːˈpɑːnɪˌʃɑːdz/; Sanskrit: उपनिषद् Upaniṣad [ˈʊpɐnɪʂɐd]) are late Vedic Sanskrit texts of religious teaching and ideas still revered in Hinduism. The Upanishads are the philosophical-religious texts of Hinduism (also known as Sanatan Dharma meaning “Eternal Order” or “Eternal Path”). The Upanishads are often called 'Vedanta'. Upanishad, one of four genres of texts that together constitute each of the Vedas, the sacred scriptures of most Hindu traditions.