A neutral density filter is a photographic accessory that reduces the intensity of light entering a camera lens without affecting the color of the light. This allows photographers to use wider apertures or slower shutter speeds in bright conditions, enabling creative effects like shallow depth of field or motion blur. These filters come in various strengths, measured in stops, which indicate how much light is blocked. By using a neutral density filter, photographers can achieve desired exposure settings while maintaining image quality, making them essential tools for landscape, portrait, and long-exposure photography.