Fill light is a type of lighting used in photography and film to reduce shadows and provide more even illumination. It complements the main light source, known as the key light, by softening harsh contrasts and enhancing details in the darker areas of a scene. Typically, fill light is softer and less intense than the key light, often created using reflectors or diffused light sources. This technique helps achieve a balanced exposure, making subjects appear more natural and visually appealing. Proper use of fill light can significantly improve the overall quality of an image or video.