In theoretical physics, a kugelblitz is a concentration of energy so intense that it creates an event horizon, a boundary in space-time where the massive gravitational pull lets nothing escape, not even information. A black hole results.
Theories predict that if enough energy (light, heat, etc.) is aimed into a region (perhaps we fire a legion of impossibly powerful lasers at a point in space), the concentration of energy can warp space-time enough for the region to become a black hole. This differs from typical black holes in that it would be the result of an incredibly large amount of energy, not an ungodly amount of matter or the implosion of a dying star.
The amount of energy required to create a kugelblitz could result in one of the hottest temperatures in the universe.