leading

In typography, leading ( ) is the space between adjacent lines of type; the exact definition varies.

In hand typesetting, leading is the thin strips of lead (or aluminium) that were inserted between lines of type in the composing stick to increase the vertical distance between them. The thickness of the strip is called leading and is equal to the difference between the size of the type and the distance from one baseline to the next. For instance, given a type size of 10 points and a distance between baselines of 12 points, the leading would be 2 points. This combination of type size and distance between baselines is described as "10 on 12 pt", which may appear in a book's colophon as "Typeset in 10 on 12 pt Times Roman", or similar.