Full Color Printing Glossary

Colour separations - "The division of a multi-coloured original or line copy into the basic (or primary) process colours of yellow, magenta, cyan and black. These should not be confused with the optical primaries; red, green and blue. Column inch - a measure of area used in newspapers and magazines to calculate the cost of display advertising. A column inch is one column wide by one inch deep."

See also:

Contrast, Halftone, Pantone, Process color separation, Secondary colors,