Definition of em in English:

em

noun

  • 1Printing
    A unit for measuring the width of printed matter, equal to the height of the type size being used.

    • ‘From there, sizing descendant elements with ems (a relative unit of measurement) becomes much more logical: 1em is 10 px, 1.6em is 16 px, .9em is 9px, and so forth.’
    • ‘Sterne was almost compulsively attentive to page layout and typography, going so far as to specify the length of each dash in printer's ems.’
    • ‘It doesn't matter which unit you use - zero horseshoes is the same as zero pixels, ems, or percentages.’
    1. 1.1A unit of measurement equal to twelve points.
      ‘So, a font size of 1.25 ems will be displayed as 1.25 pixels.’
      ‘This reduced the text to an unreadable level when the CSS specified sizes in ems, but only reduced it slightly when specified as percentages.’

Origin

Late 18th century the letter M represented as a word, since it is approximately this width.

Pronunciation

em

/ɛm/