Em quad is a typographical term that refers to a unit of measurement in printing. It is equal in width to the letter M in the typeface and size being used. Some synonyms for em quad include em-space, mutton, and en quadrat. The em-space is a term often used in digital media and refers to a horizontal space that is equal in width to a line of text. Mutton is a term that can be used interchangeably with em quad in print production. Finally, en quadrat is a similar but smaller unit of measurement, equal in width to the letter N in the typeface and size being used, which is useful in text justification.