Tracking
The uniform spacing applied across a run of letters, opening or closing the overall texture of a word or line — letter-spacing, in CSS terms.
Example usage
“Add tracking to the all-caps label — capitals need air that lowercase doesn’t.”
Editor’s note
Two rules cover most cases: track caps and small caps open, because capitals were never designed to sit side by side; track large headlines slightly negative, because display sizes accumulate visual space. Tracking lowercase body text in either direction mostly damages the rhythm the typeface was designed with. Not to be confused with kerning, which adjusts individual pairs.