What is a "brim"?

A brim is a projecting edge, rim, or margin on a hat, cap, or helmet that shades the eyes and provides protection from the sun or rain. It is usually made of the same material as the crown and can be either flat or curved. The brim's width can vary from narrow to wide, and the shape can be altered to fit the style of the hat. Brims can also be decorated with various materials such as leather, fabric, or ribbon, and can be adorned with feathers, flowers, or other accessories.