The name of the letter M. In Printing, the square, formerly of the type m, used in typography as the unit for measuring and estimating the amount of printed matter in a line, page, etc. The em of pica is the standard.
1864. Daily Tel., 3 Oct., 5/4. [The printers’ union] advanced its demands from forty-five cents to sixty cents per thousand ‘ems.’
1888. Encycl. Brit., s.v. Typography, The width of … pages … is expressed according to the number of ‘ems,’ that is of a pica ‘m’—the square of the depth of pica … A page of 24 ems wide is equal to one of 4 inches.
