Quad (typography)

The term was later adopted as the generic name for two common sizes of spaces in typography, regardless of the form of typesetting used.

Both are encoded as characters in the General Punctuation code block of the Unicode character set as U+2000   EN QUAD and U+2001   EM QUAD, which are also defined to be canonically equivalent to U+2002   EN SPACE and U+2003   EM SPACE respectively.

[a] In 1771, in the first edition of the Encyclopædia Britannica, it says:[8][b] Quadrat, in printing, a piece of metal cast like the letters, to fill up the void spaces between words, etc.

Pieces of type metal, of the depth of the body of the respective sizes to which they are cast, and lower than types, so as to leave a blank space on the paper, when printed, where they are placed: an en quadrat is half as thick as its depth; an em quadrat is equal in thickness and depth, and, being square on its surface, is the true quadrat, from quadratus, squared; a two em quadrat is twice the thickness of its depth; a three em three times; and a four em four times, as their names specify.

[...] Quadrat, kwod′rat, n. a piece of type-metal lower than the letters, used in spacing between words and filling out blank lines (commonly Quad)—distinguished as en (), em (), two-em (), and three-em ().