In Tibetan Buddhism Vajrayana , Om is often placed at the beginning of mantras and dharanis. Probably the most well known mantra is "Om mani padme hum", the six syllable mantra of the Bodhisattva of compassion, Avalokiteśvara. This mantra is particularly associated with the four-armed Shadakshari form of Avalokiteśvara. Moreover, as a seed syllable (bija mantra), Aum is considered sacred and holy in Esoteric Buddhism.
Scholars interpret the first word of the mantra "Om Mani Padmi Hum" to be AUM, with a meaning similar to Hinduism – the totality of sound, existence and consciousness.
Om has been described by the 14th Dalai Lama as "composed of three pure letters, A, U, and M. These symbolize the impure body, speech, and mind of everyday unenlightened life of a practitioner; they also symbolize the pure exalted body, speech and mind of an enlightened Buddha." According to Simpkins, Om is a part of many mantras in Tibetan Buddhism and is a symbolism for "wholeness, perfection and the infinite".
This application is intended for working with our chakras , you get seven tones of the Om mantra corresponding to each chakra in our body :