Neutral Density (ND) filters are optical devices that reduce the intensity of light entering a camera lens without affecting the color of the light. They are commonly used in photography and videography to allow for longer exposure times or wider apertures in bright conditions. This helps achieve effects like motion blur or a shallow depth of field. ND filters come in various strengths, measured in stops, which indicate how much light is blocked. For example, a 3-stop ND filter reduces light by a factor of eight, allowing photographers to control exposure settings creatively.