The sound of the universe. It's the first, original vibration, representing the birth, death, and re-birth process.
Chanting the sound OM brings us into harmonic resonance with the universe – this is a scientific fact! OM is said to vibrate at 432 Hertz, which is the natural musical pitch of the Universe, as opposed to 440 Hertz, which is the frequency of most modern music.
Decreasing your frequency to coincide with that of the Universe stills the fluctuations of the mind, allowing you to practice yoga through sound.
OM is an idyllic way to begin and end a yoga or meditation practice, and also comes in handy when you just need to relax.