As per the Shiva Purana, once Brahma (the Hindu God of creation) and Vishnu (the Hindu God of preservation) had an argument in terms of supremacy of creation. To test them, Shiva pierced the three worlds as a huge endless pillar of light, the jyotirlinga. Vishnu and Brahma split their ways to downwards and upwards respectively to find the end of the light in either direction. Brahma lied that he found out the end, while Vishnu conceded his defeat.
Shiva appeared as the second pillar of light and cursed Brahma that he would have no place in ceremonies while Vishnu would be worshipped till the end of eternity. The jyotirlinga is the supreme partless reality, out of which Shiva partly appears. The Jyotirlinga shrines, thus are places where Shiva appeared as a fiery column of light.Originally there were believed to be 64 jyotirlingas while 12 of them are considered to be very auspicious and holy. Each of the twelve jyotirlinga sites take the name of the presiding deity - each considered different manifestation of Shiv.
At all these sites, the primary image is lingam representing the beginningless and endless Stambha pillar, symbolizing the infinite nature of Shiv.
The twelve jyothirlinga are Somnath in Gujarat, Mallikarjuna at Srisailam in Andhra Pradesh, Mahakaleswar at Ujjain in Madhya Pradesh, Omkareshwar in Madhya Pradesh, Kedarnath in Himalayas, Bhimashankar in Maharashtra, Viswanath at Varanasi in Uttar Pradesh, Trimbakeshwar in Maharashtra, Vaidyanath at Deoghar in Jharkhand, Nageshwar Temple at Dwaraka in Gujarat, Rameshwar at Rameswaram in Tamil Nadu and Grishneshwar at Aurangabad in Maharashtra.
Lord Shiva showed himself as a Jyotirlinga on the night of the Aridra Nakshatra. It is believed that a person can see the Jyotirlingas as columns of fire piercing through the earth as he reaches a higher level of spiritual attainment. Each Jyotirlinga site takes the name of the presiding deity. Basically, the Jyotirlinga signifies the infinite nature of Lord Shiv. At the highest level, Shiva is regarded as formless, limitless, transcendent and unchanging absolute Brahman and the primal Atman (soul, self) of the universe.