Ok, bear with us on this one: the entire book is an elaborate extended metaphor for the path of life. Didja see that one coming?
Let's start with the basics. The kids show up in a damp, dark passage (the Box) that opens its doors into a brand new world. Sounds a wee bit like being born, doesn't it? When they emerge, they don't know anything except the simplest of facts—their names. Then, they find themselves in the Glade, a pseudo-idyllic place where it never rains, sleets, or snows. Sure it's surrounded by a super dangerous place, but if you stay inside you are sheltered against most of the threats. The older/more senior boys look after you as long as you do your job and follow the rules… this is kind of like childhood, no?
But the longer you are in the Glade, the more chance you have of becoming a Runner, and then you might enter the Maze. The Maze is adolescence: it's confusing, frustrating, and every decision you make could be hugely important (see our discussion of "The Maze" elsewhere in this section). Then you might be unfortunate enough to get stung by a Griever and go through the Changing. It's painful—both physically and emotionally—and although brief, it leaves you forever different: "Shanks who've been through it'll never really talk about it. They get…different. Unlikeable" (23.31). When you emerge from the Changing, you have new awareness of the world that surrounds you, and it might make you moody, dour, and even angry all the time. In order to pass through this difficult stage, and escape into the real world, you need to quite literally take the plunge off the Cliff.
The Cliff is like an obstacle of faith—think Indiana Jones and the Last Crusade—and you have to trust that whatever lies on the other side of the Griever Hole (adulthood) is going to be better than where you are now.
So to sum it up: Box = womb, birth into the Glade = childhood, Maze = adolescence, Changing = particularly difficult adolescence, and the "real" world = adulthood. Got it?