In photography, density is a numerical measurement that indicates the darkness of a tone on a negative, transparency, or print. Higher density values represent darker areas that transmit or reflect less light, while lower density values correspond to lighter tones. Density plays a key role in determining contrast, exposure accuracy, and tonal range, and is often measured using a densitometer. Understanding density helps photographers achieve balanced images with accurate highlights, midtones, and shadows in both film and digital workflows.