The medieval era texts of Hinduism, such as the Puranas adopt and expand the concept of Om in their own ways, and to their own theistic sects. According to the Vayu Purana, Om is the representation of the Hindu Trimurti, and represents the union of the three gods, viz. A for Brahma, U for Vishnu and M for Shiva. The three sounds also symbolise the three Vedas, namely (Rigveda, Samaveda, Yajurveda).