A jyotirlinga is a special form of Lord Shiva, appearing as a column of light. It represents his supreme and endless power.
According to the Shiva Purana, Lord Brahma and Lord Vishnu once argued about who was the greatest. To test them, Lord Shiva appeared as a huge pillar of light, called the jyotirlinga, stretching through the three worlds. Vishnu went downwards, and Brahma went upwards to find its end. Vishnu accepted that he couldn’t find it, but Brahma lied that he had.
Shiva then appeared again and cursed Brahma that he would never be worshiped in ceremonies. However, he blessed Vishnu, saying he would be worshiped forever. This story shows Shiva’s greatness and truth.