Wikipedia
Pāñcajanya (or Panchjanya) is the name of the conch (Shankha) in Hindu mythology which was blown by Krishna at the start of the Mahabharata War between the Kauravas and Pandavas at Kurukshetra, which was a Dharam-yudha (sacred war for the righteous) between the usurper King Dhritrashtra's hundred sons, the eldest being Duryodhana, and the five Pandavas (the cousins) supported by Lord Krishna himself.
Panchjanya when blown by Lord Krishna symbolised the war was won by the righteous Pandavas. Panchjanya is the udghosh, the sound of righteousness to be heard by the people of the world. Panchjanya is mentioned in the text 15 of the first chapter of Bhagavad Gita. Panchjanya, the great conch was a token of gift taken from Panchjana, the navigator in whose ship Srikrishna voyaged to rescue Sandipani's son.
It is said that when Krishna blows on His transcendental conchshell, the wives of the demons become subject to abortions, and the wives of the demigods become blessed with all auspiciousness. In this way, the sound of Krishna's conchshell used to vibrate and circulate all over the world.