Let's start with the literal level: the world outside the Dome is being torched by Dome thugs. The wretches are covered in burn marks. But those facts alone don't get to the heart of why Burn is called Burn.
You'd be hard pressed to find a word more symbolically loaded than the word "burn." On the one hand, it suggests devastation. And there's devastation a'plenty in Burn: cities are razed, the Dome is punctured, and the world inside the Dome is revealed to be built on a foundation of lies. Ouch. Burn.
But there are also a few optimistic connotations to the word "burn." For one thing, thing of the phoenix: that mythological bird tends to rise from the ashes… and you can't get ashes without a bit of pyromaniacal destruction.
And the optimism doesn't stop there. "Burn" can refer to passion. You burn with longing. You burn with purpose. Famous people are said to be "burning brightly" when they accomplish great things.
We think that the title Burn is a whole lot like the content of the novel itself. At first glance, it's pretty horrifically grim. But the longer you ponder over it, the more that nuanced glimmers of hope start to appear. Sure, the world doesn't turn paradisiacal when Burn ends. But the characters within this novel have hope and passion—they burn with the desire to change the world.
The flame of the Dome may be snuffed, but the fire within Pressia, Lyda and El Capitan burns as brightly as ever.