en space

Noun

 * 1)  A space which has a nominal width of 1 en.

Usage notes
The en quad and the en space are usually synonymous as they both start as a space with a width of 1 en. However, in electronic publishing, a few contrast the two by holding that if the font is condensed or expanded to alter the width of the characters, the en quad remains 1 en in width, while the en space is altered in width to the same proportion as the printing characters.