Om (or Aum) (listen (help·info); Sanskrit: ॐ, ओम्, romanized: Ōṃ) is the sound of a sacred spiritual symbol in Indic religions. The meaning and connotations of Om vary between the diverse schools within and across the various traditions. It is part of the iconography found in ancient and medieval era manuscripts, temples, monasteries, and spiritual retreats in Hinduism, Buddhism, Jainism, and Sikhism.^[1][2] As a syllable, it is often chanted either independently or before a spiritual recitation and during meditation in Hinduism, Buddhism, and Jainism.^[3][4]

In Hinduism, wherein it signifies the essence of the Ultimate Reality (parabrahman) which is consciousness (paramatman),^[5][6][7] Om is one of the most important spiritual symbols.^[8][9] It refers to Atman (Self within) and Brahman (ultimate reality, entirety of the universe, truth, divine, supreme spirit, cosmic principles, knowledge).^[10][11][12] The syllable is often found at the beginning and the end of chapters in the Vedas, the Upanishads, and other Hindu texts.^[12] It is a sacred spiritual incantation made before and during the recitation of spiritual texts, during puja and private prayers, in ceremonies of rites of passage (sanskara) such as weddings, and during meditative and spiritual activities such as Pranava yoga.^[13][14]

https://en.wikipedia.org/wiki/Portal:Hinduismhttps://en.wikipedia.org/wiki/Portal:Hinduism

The syllable Om is also referred to as Onkara/Omkara and Pranav/Pranava among many other names.^[15][16]

“The denial that a human being possesses a “self” or “soul” is probably the most famous Buddhist teaching. It is certainly its most distinct, as has been pointed out by G. P. Malalasekera: “In its denial of any real permanent Soul or Self, Buddhism stands alone.” A similar modern Sinhalese perspective has been expressed by Walpola Rahula: “Buddhism stands unique in the history of human thought in denying the existence of such a Soul, Self or Ātman.” The “no Self” or “no soul” doctrine (Sanskrit: anātman; Pāli: anattan) is particularly notable for its widespread acceptance and historical endurance. It was a standard belief of virtually all the ancient schools of Indian Buddhism (the notable exception being the Pudgalavādins), and has persisted without change into the modern era. […] both views are mirrored by the modern Theravādin perspective of Mahasi Sayadaw that “there is no person or soul” and the modern Mahāyāna view of the fourteenth Dalai Lama that “[t]he Buddha taught that […] our belief in an independent self is the root cause of all suffering”.”

Atman and Buddhism:

• Wynne (2011, pp. 103–105)