the complement of tracking (i.e. vertical spacing instead of horizontal) is called leading — not pronounced like “leading lady,” but the other way.
why is it pronounced like that? because in the days of physical typesetting, that was how wide the lead1 shim they had to insert between lines would have been
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why lead? presumably because you could cut it to size with hand tools, and then, when it ran out, have someone melt and recast some fresh leading out of the scrap with simple equipment
