I discovered Aum ॐ while in India in 2004 and it has been a significant part of my life since. It is often used in Yoga and meditation.
While there are 100s of meanings to the word and such symbolism that it is nearly impossible to capture the true essence of what Aum is with words, here is the beginning of some insight to Aum.
I have gathered this information via various resources (books, www, etc.) to provide a basic understanding.
The origin of Aum (also Om or, more rarely, Ohm) ॐ is Sanskrit and is a mystical or sacred syllable in the Hindu, Jain and Buddhist religions.
Aum is said to be the essence of all mantras, the highest of all mantras or divine word , ultimate reality itself. By sound and form, AUM symbolizes the infinite ultimate reality and the entire universe.
A stands for Creation
U stands for Preservation
M stands for Destruction or dissolution
The three portions of AUM relate to the states of waking, dream and deep sleep. The three letters also indicates three planes of existence, heaven , earth and netherworld.
The Music of 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, or soul.