Source : The Australian Pocket Oxford Dictionary (fourth Edition)
''What's that?'' Ralph had stopped smiling and was pointing at the lagoon. Something creamy lay among the ferny weeds ''A stone'' ''No. A shell ''. Suddenly Piggy was a-bubble with decorous excitement. S'right. It's shell! I seen one like that before. On someone's back wall. A conch he called it. He used to blow it and then his mum would come. "
At the beginning of the novel, Ralph and Piggy discover the conch shell on the beach.
They decide to use it to call other boys after the crash separates them "we can use this to call others.
After the boys assemble, the conch takes a symbolic meaning; becoming identified with "democracy and free speech'' .
The boy who holds the conch has the authority to speak, and has democratic security.