A meltdown happens when someone becomes so overwhelmed by emotions like frustration, anger, or anxiety that they lose control of their behavior. During a meltdown, a person might cry uncontrollably, shout, or even throw things. Young children often have meltdowns when they're tired, hungry, or can't have something they want. You've probably seen a toddler having a meltdown in a grocery store, screaming and kicking because they can't get candy.

Older kids and adults can have meltdowns too, though they usually look different. A student might have a meltdown when facing too much homework and too little sleep, snapping at everyone around them. An adult might have a meltdown after a terrible day at work, breaking down in tears or yelling about small problems that normally wouldn't bother them.

The word also describes what happens when a nuclear reactor's cooling system fails and the reactor core overheats dangerously, like what happened at Chernobyl in 1986. Engineers work extremely hard to prevent these disasters.

People also use meltdown more casually to describe any kind of breakdown or collapse. A company might experience a financial meltdown, or a computer system might have a meltdown and stop working. The image is always the same: something that should be stable and controlled instead falls apart dramatically.