Aum (also Om, written in Devanagari as ॐ, in Sanskrit known as praṇava प्रणव [lit. "to sound out loudly"] or auṃkāra (also as Omkāra) ओंकार (lit. "auṃ syllable") is a mystical or sacred syllable in the Indian religions, i.e. Hinduism/Sanātana Dharma, Buddhism, and Jainism.

Aum is commonly pronounced as a long or over-long nasalized close-mid back rounded vowel, [õːː]) though there are other enunciations pronounced 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 is taken to consist of three phonemes, a, u and m, variously symbolizing the Three Vedas or the Hindu Trimurti or the three stages of life ( birth, life and death ). Though ostensibly, in some traditions, it is polysyllabic and vocalized as a triphthong, the Omkāra is held to move through and contain all vowels possible in human speech, since in properly vocalizing the 'aah', 'oo' and 'mm' sounds, one's mouth perforce adopts the shapes which it would have to in order to make other phonemes as well.. One important version has five components, flowing from h through a, [short]u, oo to m.

The name Omkara (Sanskrit: the syllable aum) is taken as a name of God in the Hindu revivalist Arya Samaj (ārya samāj. Similarly, the concept of om, called onkar in Punjabi, is found in Sikh theology as a symbol of God. It invariably emphasizes God's singularity, expressed as Ek Onkar ("One Omkara" or "The Aum is One"), stating that the multiplicity of existence symbolized in the aum syllable is really founded in a singular God.