In typography, a quad (originally quadrat) was a metal spacer used in letterpress typesetting. The term was later adopted as the generic name for two common sizes of spaces in typography, regardless of the form of typesetting used. An em quad is a space that is one em wide; as wide as the height of the font. An en quad is a space that is one en wide: half the width of an em quad.
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.
- Sassoon, Rosemary (1993). Computers and Typography, v.1. Intellect. p. 40. ISBN 1871516234.
- Jukka Korpela. "Unicode Spaces". Archived from the original on 2021-09-02. Retrieved 2013-09-18.
- Unicode Consortium. "The Unicode Standard, Version 6.2: General Punctuation, Range 2000–206F" (PDF). Retrieved 2013-09-18.
- "Unicode Mail List Archive: RE: Difference between EM QUAD and EM SPACE". unicode.org. Retrieved 2021-06-05.