Quad (typography)
In typography, a quad 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.
