The most sacred of Hindu symbols, Aum (Om), is thought to represent both the visible and invisible parts of the omnipresent, omniscient, and omnipotent God. It represents a number of important triads, including the three worlds (earth, heaven, and atmosphere); the three holy Vedic writings (Yajur, Sama, and Rig); and the three primary Hindu Gods (Brahma, Vishnu and Mahesh or Shiva). Om is also regarded as the most sacred of sounds, as it is the source from which the universe and all of existence arose, and it is the glue that ties everything together. All Hindu prayers, meditations, and rituals begin and end with the chanting of this magical phrase.