The most sacred symbol in Hindu dharma. Aum (OM) is the sound of the infinite.
Aum is said to be the essence of all mantras, the highest of all matras or divine word (shabda), brahman (ultimate reality) itself. Aum is said to be the essence of the Vedas.
By sound and form, AUM symbolizes the infinite Brahman (ultimate reality) and the entire universe.
A stands for Creation.
U stands for Preservation.
M stands for Destruction or dissolution.
This is representative of the Trinity of God in Hindu dharma (Brahma, Vishnu and Shiva).
The three portions of AUM relate to the states of waking, dream and deep sleep and the three gunas (rajas, satva, tamas).
The three letters also indicates three planes of existence, heaven (swarga), earth (martya) and netherworld (patala).
All the words produced by the human vocal organ can be represented by AUM. A is produced by the throat, U & M by the lips.
In the Vedas, AUM is the sound of the Sun, the sound of Light. It is the sound of assent (affirmation) and ascent (it has an upwards movement and uplifts the soul, as the sound of the divine eagle or falcon.