In photography

Photography

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

, a snoot is a tube or similar object that fits over a studio light or portable flash

Flash (photography)

A flash is a device used in photography producing a flash of artificial light at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light...

and allows the photographer to control the direction and radius of the light beam. These may be conical, cylindrical, or rectangular in shape. Snoots can isolate a subject when using a flash. They help by stopping "light spill", or when lighting falls in a larger footprint than intended.