em

OBS: L'équivalent proposé, «em» désigne une notion purement nord-américaine, l'«em» n'étant pas utilisé en Europe.

OBS: Because the term dates back to hand composition and the use of square metal type, most sources still refer to the em as being a square area. Thus, an em is often defined as the square of the point size of a given face. The em for a twelve-point size (i.e. a 12-point em) would be 12 points wide and 12 points deep. So called because it is the rectangular area occupied by the capital M of the typeface.
OBS: The unit em has no precise meaning without indication of its body size because the actual area of an em, expressed in points, changes with the type size. The proportion, however, always remains the same. If printers speak of ems without adding a specific body size, they usually mean the pica, or 12-point, em.