Basically, the Killballs are ball shaped spheres (duh?) that insta-kill anything on contact. If you drive a Warthog inside, it'll explode. If an Elite rubs up against its orange exterior, it'll die a quick death. If a Scorpion enters Killball territory, you'll witness its destruction and the resulting turret ejection. You get the point. Killballs kill.
Nestled between the Flood-like skin folds of the Bungie Weekly Update are details about the recent Mythic Map previews, upcoming playlist changes, how the Sandbox Forge budget will function and Bungie squashes nearly every rumor regarding Sandbox's icy blue grid lines. Knowledge is power. More power can be obtained here.