Om

Om is a polysemous symbol representing a sacred sound, seed syllable, mantra, and invocation in Hinduism as well as in other Indian religions. Its written form is the most important symbol in the Hindu religion. It is the essence of the supreme Absolute, consciousness, Ātman, Brahman, or the cosmic world. In Indian religions, Om serves as a sonic representation of the divine, a standard of Vedic authority and a central aspect of soteriological doctrines and practices. It is the basic tool for meditation in the yogic path to liberation. The syllable is often found at the beginning and the end of chapters in the Vedas, the Upanishads, and other Hindu texts. It is described as the goal of all the Vedas. Read more on Wikipedia