The Brahmavidya Upanishad (Sanskrit: ब्रह्मविद्या उपनिषत्, IAST: Brahmavidyā Upaniṣad) is a Sanskrit text and one of the minor Upanishads of Hinduism. It is one of twenty Yoga Upanishads in the four Vedas.

The Upanishad mainly explains the structure of Om, aspect of its sound, its placement, its beginning and end, and the significance of the Laya (fading away of its sound).Om is Brahman (ultimate reality), asserts the text.The text is notable for stating that gods live inside human body as five Atmans, with Vishnu in the throat, Rudra in the middle of the palate, Shiva in the forehead, Sadashiva at the tip of nose, and the Brahman in the heart. The innermost Atman, states the text, is same as the all transcendent Paramatman, the Brahman pervading everywhere.

Ref: Wikipedia