Magenta
Also known as process red; one of the 4 basic ink colors in process color printing;
M in abbreviation CMYK
Mask
Blocking light from reaching parts of a printing plate, also called knockout
Matte
Dull non-glossy finish
Micrometer
Devise used to measure the thickness (caliper) of paper
Middle tones
The tones in a photograph between highlights and shadows; must be balanced for accurate reproduction
Moire
An undesirable screen pattern caused by incorrect screen angles