Who are the choir on the island in "Lord of the Flies"?
The choir are just the boys who arrive with Jack. It's common in English private schools for there to be an all-male choir, and clearly Jack was the leader or the head boy (he wears a golden badge). Choirboys are traditionally a symbol of goodness, religious purity and innocence - and do note that, when they arrive, Jack's choir all wear their uniforms:
each boy wore a square black cap with a silver badge in it. Their bodies, from throat to ankle, were hidden by black cloaks which bore a long silver cross on the left breast.
Also - rather brilliantly, I think - it means that the descent into devilish savagery for Jack and his gang starts from the highest possible point: a group of innocent, angelic, beautiful-sounding choirboys become a savage, animalistic-sounding group of murderers.
Peter Brook makes a lot of the image of choirboys in his film of the novel (made in the 1960s).