The space between words in a line of type. In the days of metal type, word spacing was achieved by putting pieces of metal between the individual letters that made up words. In word spacing, these pieces of metal were called quads. All were related in size to the “em quad,” which is the square of the type size. For example, if the type is 10 point, the em quad is a square 10 points by 10 points; if the type is 72 point, the em quad is 72 points square (it was called the em quad as the capital M of most typefaces were set in a square piece of metal, with the height and width being equal). Since 1 em quad would be too much space between words, smaller pieces of metal, which are subdivisions of the em quad, were used. One third of an em is considered normal word spacing.