An earflap is a flap of fabric attached to a winter hat that folds down to cover your ears and keep them warm. You've probably seen earflaps on those classic trapper hats or aviator caps: they hang down on both sides and can be tied under your chin or folded up on top of the hat when you don't need them.

Earflaps became popular on hats worn by pilots, explorers, and people working in extremely cold conditions because exposed ears are particularly vulnerable to frostbite. Your ears stick out from your head and don't have much fat to protect them, so they get dangerously cold faster than other body parts.

Most winter hats with earflaps let you adjust them depending on the weather. On a brutally cold morning waiting for the school bus, you pull them down and tie them snugly. When you get too warm playing outside or step into a heated building, you can flip them back up. Some earflaps have fur lining for extra warmth, while others use fleece or wool.

The individual parts of your outer ear are sometimes called earflaps too, though doctors usually call them auricles or pinnae. But when someone mentions earflaps in everyday conversation, they almost always mean the warm, protective flaps on a winter hat.