the lord of the flies is the sow's head on the stick that Jack put up as an offering to the "beastie." The Lord of the flies is the literal translation of the Hebrew word 'Beelzebub', a Satan figure...
The lord of the flies is a pigs head on a stick. the "lord of the files" translates to Beelzebub which means the devil. so the head on the stick is showing the evil on the island.
in lord of the flies, the pig that the kids killed is the lord of the flies. it is a pig on a stick sharpened at both ends and it ends up rotting, and then flies swarm it. that is how it got its name.