Om or Aum is a mystical sacred syllable that is pronounced as a long close-mid back rounded vowel.
When do you Om in Yoga?
Typically, the Yoga practice begins and ends with Om but not always. It really just depends on the instructor as to whether or not you use this. It’s an awesome feeling, though, when the room reverberates with this particular sound.
So…this is all cool but what is the significance?
It roughly represents both the unmanifest (nirguna) and manifest (saguna) aspects of God. That is why it is also in some texts called pranava, to mean that it pervades all life (what is seen and unseen) and runs through our prana or breath.
Here’s what Patanjali says in Sutra 1:27 about Om (shortened and your translation might be a little different depending on which Yoga Sutra book you happen to be reading)
Om is a sacred mantra. The sound vibration is at the source of all creation; vibration, being the subtlest form of creation, is the nearest we can get to enlightenment in the physical world. Om represents the individual self and the universal soul becoming one. Om or Aum is composed of 3 syllables a, u, m. They are universal and therefore are the seed (bija) of all words. “A” symbolizes speech, “u” is mind and “m” is breath of life. Aum is the everlasting spirit, a symbol of serenity, divinity, majestic power, omnipotence and universality.