Pranava yoga is meditation on the sacred mantra Om, as outlined in the Upanishads, the Bhagavad Gita, and the Yoga Sutras of Patanjali. It is also called Aum yoga and Aum yoga meditation. It is, simply put, fixing the mind on the sound of the mantra "Aum" – the sacred syllable that both symbolizes and embodies Brahman, the Absolute Reality – as the mantra is constantly repeated in unison with the breath. The purpose of pranava yoga is to become free from suffering and limitation.
The purpose is well stated in the Prashna Upanishads:
"What world does he who meditates on Aum until the end of his life, win by That? If he meditates on the Supreme Being with the syllable Aum, he becomes one with the Light, he is led to the world of Brahman [the Absolute Being] Who is higher than the highest life, That which is tranquil, unaging, immortal, fearless, and supreme."
— Prashna Upanishad 5:1.5.7