Question

What are upanishads?

Answer 1

A Upanishads are religious and sacred books that Hindus believed in.

They also  contain some of the central philosophical concepts and ideas of Hinduism, some of which are shared with religious traditions like Buddhism and Jainism.

Answer 2

the term Upanishad literally means sitting close to or down near.
the upanishad are the collection of books originally written in the Sanskrit language .