Color banding
From The Glossary of Digital Photography
When bands of color are seen instead of smooth changes within an image. This especially appears in portions of images that have areas of smooth color, such as skies. Color banding tends to be less obvious with 16-bit images than with 8-bit images. Dithering is used in digital printing to reduce the appearance of color banding. See also 16-bit color; 8-bit color; dithering
