D-min (short for minimum density) refers to the lightest part of an image or negative-the area that transmits or reflects the most light. It defines the base level of brightness in a photograph and plays an important role in determining the overall contrast and tonal range. Lower D-min values allow for brighter highlights and subtle detail in light areas, helping photographers achieve balanced exposures and high-quality prints. Understanding D-min is essential when evaluating film, prints, or digital scans to ensure accurate reproduction of highlights and midtones.