Banding
From The Glossary of Digital Photography
A digital artifact or specific type of noise that often appears as noisy stripes in generally smooth areas of an image or print. Banding is usually most visible in the shadows and at high ISO settings. If the banding occurs in the original digital image, software options exist that can help eliminate or reduce the problem. Working in raw format will often help, since the photographer will have between 12 and 16 bits, instead of 8, leading to more values for each pixel. Sometimes the banding takes the form of posterization. A clogged jet or running out of a color of ink can cause banding in an inkjet print. The printer's ink levels should be checked and a nozzle check run to find the problem. See also noise
