Meaning
Written AUM, the sound opens at the back of the throat with A, rolls forward through U, and closes at the lips with M, then rests in silence. The Mandukya Upanishad matches those parts to waking, dreaming, and dreamless sleep, and the silence to turiya, the fourth. Called pranava, that which is sounded forth, it is treated not as a word but as the whole of speech in one syllable.
ॐ, सम्पूर्ण सृष्टि का मूल नाद।