The Lord of the Flies has two significant meanings:
First, it is a direct allusion to the Devil, which we could argue represents evil. This object represents evil creeping into each of the boys. When Simon confronts it and seems to have a hallucination, we see a physical dilemma Simon encounters as a result of having been enlightened by the dead man whose parachute hangs in the trees. The more Simon knows the truth, the more evil tries to destroy him. The power of evil becomes greater throughout the story as this object seems to have more power over the boys.
Next, the Lord of the Flies is literally a pig's head that attracts a bunch of flies. This is much like the boys are attracted to a life of savagery, and then, like flies they go all over the place and feel a little crazy.
There are so many parallels to evil and levels of the depth of understanding the symbolism that it can certainly be taken too far. Take a look at the description at the link below for symbolism.