It is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition.

Neutral density (ND) filters reduce the amount of light entering the camera, enabling a longer exposure time than otherwise possible. This can emphasize motion, or make an otherwise tumultuous scene appear surreal and quiescent. They are especially useful in bright light conditions to help prevent overexposure. Neutral Density filters also allow proper exposure at a wider lens opening for reduced depth-of-field to highlight a key subject by making the foreground and/or background out of focus. ND filters are also one of the easiest filters to use, and their effect cannot be replicated digitally — at least not with a single shot.