of relative distance in typography
, one em being equivalent
to the point size
of the type. In 8 point type, an em is 8 point wide; in 9 point type, 9 point wide; in 10 point type, 10 point wide ... and so on. So named because traditionally it is defined as the width of a capital
'M' in the face
and point of type being used. See also en.