Word Spacing
http://www.itcfonts.com/Ulc/2911/WordSpacing.htm

Strizver, Ilene
Upper and lowercase Magazine
2003

Abstract:

When setting type, most of us are very conscious of type style, size, width and line spacing. Many of us also pay attention to letter spacing and kerning, even if we’re not as confident in these areas. But word spacing--the space between words--is probably the most neglected of typographic attributes. This seemingly small detail plays an important role in the color, texture and readability of your type.