The vertical distance between lines of text, measured baseline to baseline: line-height, in CSS terms.
Open up the leading on the intro paragraph. At 1.2 the lines feel stacked, not set.
Pronounced “ledding,” after the strips of lead once placed between lines of metal type. Body text wants roughly 1.4 to 1.6× the type size; headlines want much less. Large sizes accumulate vertical space, and loose leading makes a two-line headline fall apart into two separate thoughts.