Oṃ

Oṃ is the praṇava — the sacred syllable representing Brahman, the absolute reality. Composed of sounds A + U + M, representing the three states of consciousness (waking, dream, deep sleep) and the silence that pervades them (turīya). The Māṇḍūkya Upaniṣad is entirely dedicated to the analysis of Oṃ. All Vedānta study begins and ends with Oṃ.