A thunderclap is the sudden, sharp crack or rumbling boom you hear during a storm when lightning strikes. The sound happens because lightning is incredibly hot (hotter than the surface of the sun!) and instantly heats the air around it. That air expands so fast it creates a shock wave, like a sonic boom, that travels to your ears as thunder.

If you're close to where lightning strikes, you hear a quick, startling crack. If you're farther away, the sound becomes a long, rolling rumble because the sound waves bounce off clouds, hills, and buildings before reaching you. You can actually estimate how far away lightning struck by counting the seconds between the flash and the thunderclap, then dividing by five. That tells you roughly how many miles away the strike was.

The word can also describe anything sudden and dramatic that gets everyone's attention, like a thunderclap of applause when a performer finishes an amazing act, or thunderclap news that surprises everyone at once.