Om or Aum (also About this sound Auṃ (help·info), written in Tamil as ஓம் Devanāgari as ॐ and as ओ३म् or ओम्, in Sanskrit known as praṇava प्रणव (lit. "to sound out loudly"), Omkara, or Auṃkāra (also as Aumkāra) ओंकार (lit. "Auṃ form/syllable"), is a sacred or mystical syllable in most Dharmic or Indian religions, specifically Hinduism, Jainism and Mahayana Buddhism.

Om is pronounced as ओ३म् where ३ is Pluti, (indicating a length of three morae) (long or over-long nasalized close-mid back rounded vowel, [õːː]), like OOOM, दीर्घ O, though there are other enunciations adhered to in received traditions. It is placed at the beginning of most Hindu texts as a sacred incantation to be intoned at the beginning and end of a reading of the Vedas or prior to any prayer or mantra. The Māndukya Upanishad is entirely devoted to the explanation of the syllable. The syllable consists of three phonemes, a Vaishvanara,u Hiranyagarbha and m Iswara, which symbolize the beginning, duration, and dissolution of the universe and the associated gods Brahma, Vishnu, and Shiva, respectively.The name Omkara is taken as a name of God in the Hindu revivalist Arya Samaj.(wikipwdia)