Aum (also Om) is a mystical or sacred syllable in the Indian religions. It is placed at the beginning of most Hindu texts as a sacred exclamation to be uttered at the beginning and end of a reading of the Vedas or previously to any prayer or mantra. The Mandukya Upanishad is entirely devoted to the explanation of the syllable. Origin, name and written symbols
With preceding a or ā, the o of om in Sanskrit grammar in sandhi (Sanskrit: संधि, "joining") does not form vriddhi (au) but guna (o) per Pāṇini 6.1.95.
The Sanskrit name for the syllable is praṇava, from a root nu "to shout, sound, praise", verbal pra-nu- being attested as "to make a humming or droning sound" in the Brahmanas, and taking the specific meaning of "to utter the syllable om" in the Chandogya Upanishad and the Shrauta Sutras. More rarely used terms are akṣara or ekākṣara, and in later times omkāra becomes prevalent.
A popular depiction of the Aum syllable in the Devanagari script () is a ligature of ओ+ँ(oṃ, encoded in Unicode at U+0950 ॐ, the Tibetan script variant ༀ at U+0F00, and the Chinese 唵 at U+5535 or 吽 at U+543D).
It is also believed that after a very long time of meditation the Purusha Sukta revealed the word AUM as being the truth.
In Tamil language "Om" (Tamil: ஒம்) literally means "Yes", "Yes, it is".
 In Hinduism
The syllable Aum is first described as all-encompassing mystical entity in the Upanishads. Today, in all Hindu art and all over India and Nepal, 'Aum' can be seen virtually everywhere, a common sign for Hinduism and its philosophy and mythology.
Omkar Mantraha, Gayatri Chhand, Parmatma Rishi, Antaryami Devta, Ishwarpraapti arthe, jape viniyogaha. ॐ कार मन्त्रः, गायत्री छ्न्दः, परमात्मा ऋषिः, अंतर्यामी देवता, इश्वरप्राप्ति अर्थे, जपे विनियोगः
 Upanishads and Sutra literature
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.
The Katha Upanishad has: "The goal, which all Vedas declare, which all austerities aim at, and which humans desire when they live a life of continence, 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." (1.2.15-17)
The Chandogya Upanishad (1.1.1-1) states: om ity etad akṣaram udgītham upāsīta / om iti hy udgāyati / tasyopavyākhyānam "The udgitha ["the chanting", that is, the syllable om] is the best of all essences, the highest, deserving the highest place, the eighth."
The Bhagavad Gita (8.13) has: Uttering the monosyllable Aum, the eternal world of Brahman, One who departs leaving the body (at death), he attains the superior goal.
The Yoga Sutras of Patanjali states in verse (1:27): "tasya vacakah pranavah" which translates as, "God's voice is Aum."
In the following sutra it emphasizes, "The repetition of Om should be made with an understanding of its meaning".
 Puranic Hinduism
In Puranic Hinduism, Aum is the mystic name for the Hindu Trimurti, and represents the union of the three gods, viz. a for Brahma, u for Vishnu and m for Mahadev which is another name of Shiva. The three sounds also symbolize the three Vedas (Rigveda, Samaveda, Yajurveda).
According to Hindu philosophy(see Mandukya Upanishad), 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. More broadly, 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.
Vaishnava Dvaita philosophies teach that '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 Sridhara Svami the pranava has five parts: A, U, M, the nasal bindu and the reverberation (nada). Liberated souls meditate on the Lord at the end of that reverberation. For both Hindus and Buddhists this syllable is sacred and so laden with spiritual energy that it may only be pronounced with complete concentration.
In 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. Essentially, upon moksha (mukti, samadhi) one is able not only to see or know existence for what it is, but to become it. When one gains true knowledge, there is no split between knower and known: one becomes knowledge/consciousness itself. In essence, Aum is the signifier of the ultimate truth that all is one.
Examples of Three into One: Creation (Brahma)- Preservation (Vishnu)- Destruction (Shiva) into Brahman Waking- Dreaming- Dreamless Sleep into Turiya (transcendental fourth state of consciousness) Rajas (activity, heat, fire) - Tamas (dullness, ignorance, darkness) - Sattva (purity, light, serenity/shanti) into Brahman Body, Speech and Mind into Oneness
 In proper names
When Aum is a part of a place name (for example Omkareshwar), or is used as a man's name, it is spelled phonetically using ordinary letters of whatever Indian alphabet is used in the area. The adherents of Arya Samaj always use the ordinary letters अ, ऊ and म to write Aum.
 In Jainism
In Jainism, Aum is regarded to be a condensed form of reference to the five parameshthis, by their initials A+A+A+U+M (o3m). The Dravyasamgrah quotes a Prakrit line: ओम एकाक्षर पञ्चपरमेष्ठिनामादिपम् तत्कथमिति चेत "अरिहंता असरीरा आयरिया तह उवज्झाया मुणियां" oma ekākṣara pañca-parameṣṭhi-nāmā-dipam tatkabhamiti ceta "arihatā asarīrā āyariyā taha uvajjhāyā muṇiyā" "Aum" is one syllable made from the initials of the five parameshthis. It has been said: "Arihanta, Ashiri, Acharya, Upadhyaya, Muni" .
Thus, ओं नमः (oṃ namaḥ) is a short form of the Navkar Mantra.
 In Buddhism
Buddhists place om at the beginning of their Vidya-Sadaksari or mystical formulary in six syllables (viz., om mani padme hum) As a seed syllable (bija mantra), it is also considered holy in Esoteric Buddhism.
With Buddhism's evolution and breaking away from Vedic/Hindu tradition, Aum and other symbology/cosmology/philosophies are shared with the Hindu tradition. This character often appeared as "唵" in Buddhist scripts in East Asia.
 See Also