What is a "deerstalker"?

A deerstalker is a type of cap that is typically made of wool and is associated with hunting and outdoor activities. It is characterized by its distinctive shape, which features two side flaps that can be tied under the chin to protect the ears from the cold. The flaps also have a practical purpose in that they help to keep the cap in place while the wearer is active. The deerstalker is most commonly associated with the fictional detective Sherlock Holmes, who was often depicted wearing one in adaptations of the stories. It has since become a popular style of cap for outdoor enthusiasts and hunters.