Hibernate means to spend the winter in a special kind of deep rest. Many animals hibernate when food becomes scarce and temperatures drop. Bears are famous hibernators: they eat heavily in autumn, building up fat reserves, then retreat to dens where they rest through the coldest months. During hibernation, an animal's heart rate slows dramatically, its body temperature drops, and it burns very little energy. This allows creatures like groundhogs, bats, and chipmunks to survive winter without needing to hunt or forage in harsh conditions.

Hibernation is much deeper than ordinary sleep. A hibernating animal is so deeply at rest that it's difficult to wake up, and some animals don't wake until spring arrives. Their bodies enter a state almost like suspended animation, living off stored fat until warm weather returns and food becomes available again.

People sometimes use hibernate playfully to describe staying indoors during cold weather. You might say your family hibernates during a snowstorm, watching movies and drinking hot chocolate instead of going outside. Scientists and engineers also borrowed the word: computers can hibernate by saving their work and shutting down to save power, then waking up exactly where they left off.