Lightning is a powerful burst of electricity that flashes through the sky during thunderstorms. When storm clouds build up huge amounts of electrical charge, lightning releases that energy in a brilliant streak that can be several miles long and five times hotter than the surface of the sun.

The flash happens so fast that we see it almost instantly, but the sound of thunder takes longer to reach us because light travels much faster than sound. That's why you can count the seconds between lightning and thunder to estimate how far away the storm is: every five seconds equals about one mile.

Lightning usually strikes from clouds to the ground, but it can also jump between clouds or even shoot upward from tall buildings. Benjamin Franklin famously showed that lightning was electricity in 1752 with his kite experiment, which led to the invention of lightning rods that protect buildings by giving lightning a safe path to the ground.

The word also describes anything extremely fast. When someone moves like lightning, they're incredibly quick. Lightning-fast reflexes help athletes catch a ball or dodge in a game. And when something happens with lightning speed, it occurs almost too quickly to see or comprehend.