A "cap" is a type of headwear that typically has a rounded top and a visor or brim. It is often made from various materials like cotton, wool, or synthetic fabrics. Caps are commonly worn for protection against the sun, to keep warm, or as a fashion accessory. They come in many styles, including baseball caps, snapbacks, and beanies. Caps can also refer to a limit or maximum amount, such as a spending cap or a cap on emissions. In this context, it is used to control or restrict certain activities or quantities. For example, a government might impose a cap on carbon emissions to help combat climate change.