Moire pattern
From The Glossary of Digital Photography
An interference pattern that occurs when two different grid patterns are combined. This can occur in a scan of a halftone image or in a digital image of a fine pattern such as a herringbone suit. In the case of the digital image, the CCD-array pattern registers interference relative to the pattern of the fabric. The moire artifacts are considered undesirable and are to be avoided when possible. There are some software techniques, such as blurring, designed to minimize this problem after the fact. Changing the angle and the lighting at the time of the photography, or changing the screen angles and halftone frequencies in printing
can sometimes be helpful in reducing moire.
