A visor is a stiff brim that sticks out from the front of a cap or helmet to shade your eyes from the sun. Baseball caps have visors that help players see the ball on bright days. Football helmets can have clear plastic visors that protect players' eyes while still letting them see the field.

The word comes from medieval knights' helmets, which had a hinged piece called a visor that could flip down to protect the face during battle. Knights would raise their visors to see better or to show they came in peace.

Today, you'll also see separate visors that clip onto a headband, popular with tennis players and golfers who want sun protection but prefer to keep the top of their head cool and uncovered. Car sun visors flip down from above your windshield to block glaring sunlight when you're driving toward the sunrise or sunset.

Visors work by creating shade, the same way holding your hand above your eyes helps you see better in bright light. Whether it's attached to a cap, a helmet, or worn on its own, a visor's job is always the same: keeping bright light out of your eyes so you can see what you're doing.