According to the Mandukya Upanishad,"Om is the one eternal syllable of which all that exists is but the development. The past, the present, and the future are all included in this one sound, and all that exists beyond the three forms of time is also implied in it".
Om is not a word but rather an intonation, which, like music, transcends the barriers of age, race, culture and even species. It is made up of three Sanskrit letters, aa, au and ma which, when combined together, make the sound Aum or Om. It is believed to be the basic sound of the world and to contain all other sounds. It is a mantra or prayer in itself. If repeated with the correct intonation, it can resonate throughout the body so that the sound penetrates to the centre of one's being, the atman or soul.
There is harmony, peace and bliss in this simple but deeply philosophical sound. By vibrating the sacred syllable Om, the supreme combination of letters, if one thinks of the Ultimate Personality of Godhead and quits his body, he will certainly reach the highest state of "stateless" eternity, states the Bhagavad Gita.
Om" is the sound of a thoughtless state of mind—a present that is free from all tensions of life—the way to touch the depths of our real selves in its purest form.