Omkāra is the chanting of the sound Om which according to various philosophies is the primordial sound/vibration from which every form emanates.

In Hinduism, the conch is held in the hand by the symbolic depictions of various Gods, and represents the sound of Om.

This is because the sound produced by the conch resembles the Omkāra, and even when one puts their ear next to a conch without blowing it, one can hear a very subtle Om sound owing to the hollow structure of this beautiful instrument of nature.