This fancy word refers to the area where the islands duke it out. There are no natural obstacles in this space, but there are threats: The battle area is marked off with two lines, indicating high and low altitude boundaries. Dropping outside the safe space will case damage to all blocks on your island. While not immediately lethal, the damage stacks and the further you go, the more damage you incur. Given how unwieldy giant chunks of earth can be, accounting for both and recoil from weapons is not merely recommended - it's mandatory.