You can approach this title on a few different levels. To begin, “the Lord of the Flies” is the name of the pig’s head after being impaled on a stick. This seems a natural choice of names for such a bloody object. The pig’s head then, being the title and all, becomes rather important. The horrible and primitive violence of the boys is a central theme.
Next, you can approach the individual meaning and aesthetic of the words “Lord of the Flies.” “Lord” has a lot to do with power, and it is, of course, the desire for power that drives a lot of the boys of the island (think Jack and his “you’re not the boss of me” attitude). “Flies,” on the other hand, connote death and decay (think that dead squirrel you found in the backyard and all the flying insects swarming about). Put them together, and you’ve got death and decay tied up with power and corruption. Nice.
Lastly, as if that were not enough, “The Lord of the Flies” is also the name of Beelzebub, a demon or the devil, depending on how you like your mythology. So this book is getting at some pretty big questions, and driving home a rather weighty message about inherent evil and eternal darkness.