A flash unit is a device used in photography to produce a brief burst of light, helping to illuminate a scene or subject. This is especially useful in low-light conditions or when capturing fast-moving subjects. Flash units can be built into cameras or used as external accessories, providing photographers with flexibility in lighting their images. There are different types of flash units, including speedlights, studio strobes, and ring flashes. Each type serves specific purposes, such as enhancing portrait photography or providing even lighting for macro shots. Proper use of flash units can significantly improve the quality of photographs.