Om (Aum)

Om or aum is a sacred Hindu symbol, and is considered greatest of all mantras and sacred formulas. The syllable consist of three phonemes a-u-m (in Sanskrit, the vowels a and u combine to become o) and the symbol’s threefold nature is central to the meaning of Om or Aum. Aum is said to be the primordial sound that was present at the creation of the universe. It is said to be the original sound that contains all other sounds, all words, all languages and all mantras. It is a mystical or sacred syllable in the Indian religions, including Hinduism, Sikhism, Jainism, and Buddhism.
It represent several important triads like
the three worlds – earth, atmosphere, and heaven
the three major Hindu gods – Brahma, Vishnu, and Siva
the three sacred Vedic scriptures – Rigved, Yajurved, and Samaved
the three stages of life – birth, life and death
Thus Om mystically embodies the essence of the entire universe. It is uttered at the beginning and end of Hindu prayers, chants, and meditation and is freely used in Buddhist and Jain ritual also. The Mandukya Upanishad is entirely devoted to the explanation of the syllable.
The syllable is mentioned in all the Upanishads, specially elaborated upon in the Taittiriya, Chandogya and Mandukya Upanishad set forth as the object of profound religious meditation, the highest spiritual efficacy being attributed not only to the whole word but also to the three sounds a (a-kāra), u (u-kāra), m (ma-kāra), of which it consists. A-kara means form or shape like earth, trees, or any other object. U-kara means formless or shapeless like water, air or fire. Ma-kara means neither shape nor shapeless (but still exists) like the dark matter in the Universe. When we combine all three syllables we get AUM which is a combination of A-kara, U-kara, andMa-kara.
The Katha Upanishad: “The goal, which all Vedas declare, which all austerities aim at, and which humans desire when they live a life of conscience, I will tell you briefly it is Aum” .”The one syllable [evākṣara, viz. Aum] is indeed Brahman. This one syllable is the highest. Whosoever knows this one syllable obtains all that he desires.”This is the best support; this is the highest support. Whosoever knows this support is adored in the world of Brahma.”
The Chandogya Upanishad chanting the syllable om is the best of all essences, the highest, deserving the highest place, the eighth.”
In Bhagwat Gita Krishna says to Arjuna – “I am the father of this universe, the mother, the support and the grandsire. I am the object of knowledge, the purifier and the syllable Oḿ. I am also the Ṛig, the Sāma and the Yajur Vedas.”
According to Hindu philosophy, the letter A represents creation, when all existence issued forth from Brahma’s golden nucleus; the letter U refers to Vishnu the God of the middle who preserves this world by balancing Brahma on a lotus above himself, and the letter M symbolizes the final part of the cycle of existence, when Vishnu falls asleep and Shiva has to breathe in so that all existing things have to disintegrate and are reduced to their essence to him
According to Vaishnava Dvaita ‘Aum’ is an impersonal sound representation of Vishnu/Krishna while Hari Nama is the personal sound representation. A represents Krishna, U Srimati
Radharani and M jivas
According to Advaita philosophy it is frequently used to represent three subsumed into one, a common theme in Hinduism. It implies that our current existence is mithyā and maya, “falsehood”, that in order to know the full truth we must comprehend beyond the body and intellect the true nature of infinity. Aum is the signifier of the ultimate truth that all is one.
In Jainism, Aum is regarded to be a condensed form of reference to the five parameshth is, by their initials A+A+A+U+M (Arihanta, Ashiri, Acharya, Upadhyaya, Muni)
In sikhism, Ik Onkar is the first phrase in the Mul Mantra which means”there is only one God”.
Buddhists place Om at the beginning of their Vidya-Sadaksari or mystical formulary in six syllables (viz., om mani padme hum) as well as most other mantras and dharanis.
Detail description of om.
The syllable om consist of 3 curves (1,2,3), a semi circle (4)and a dot.

Curve 1, which is lower, is the largest, this symbolises the waking (jagrit) st
age. in this state the consciousness is turned outwards through the gates of the senses. The larger size signifies that this is the most common state of the human consciousness.
Curve 2, which is upper signifies the state of deep sleep (sushupti) or the unconscious state. This is a state where the sleeper desires nothing nor beholds any dream.
Curve 3, which is middle one and signifies the dream state (swapna). This is the stage which lies between deep sleep and the waking state. In this state the consciousness of the individual is turned inwards, and the dreaming self beholds an enthralling view of the world behind the lids of the eyes.
Thus these three curves represents the three states of an individuals consciousness, and the entire manifested reality spring (emerge) from consciousness hence the 3 curves represents entire physical phenomenon.
The dot signifies the fourth state of consciousness, known as turia in Sanskrit. In this state the consciousness looks neither outwards nor inwards, nor the two together. It signifies the coming to rest of all differentiated, relative existence This utterly quiet, peaceful and blissful state is the ultimate aim of all spiritual activity.
Finally, the semi circle symbolizes maya and separates the dot from the other three curves. Thus it is the illusion of maya that prevents us from the realization of this highest state of bliss. The semi circle is open at the top, and does not touch the dot. This means that this highest state is not affected by maya. Maya only affects the manifested phenomenon.