Magenta:
Process red, one of the basic colors in process color.

Makeready:

All the activities required to prepare a press for printing.

Marginal words:

Call outs for directions on various parts of a business form.

Mask:

Blocking light from reaching parts of a printing plate.

Matchprint:

Trade name for 3M integral color proof.

Matte finish:

Dull paper or ink finish.

Mechanical:

Camera ready art all contained on one board.

Mechanical separation:

Mechanical art overlay for each color to be printed.

Micrometer:

Instrument used to measure the thickness of different papers.

Middle tones:

The tones in a photograph that are approximately half as dark as the shadow area.