What is Leading?
Leading is the vertical space between adjacent lines of text, it is also called line spacing. Leading directs our eye horizontally along the text line.
In hand typesetting, leading is the thin strips of lead or aluminum, that were inserted between lines of type in the composing stick to increase the vertical distance between them.
The thickness of a strip is called leading and is equal to the distance from one baseline to the next. For example, given a type size of 10 points and a distance between baselines of 12 points, the leading would be 2 points.
By default, leading is a character attribute, which means you can apply more than one leading value to the same paragraph. The largest leading value in any type of row determines the leading value for that row. However, you can select a priority option to apply to the entire paragraph rather than to the text within a paragraph. This setting does not affect leading in the current frame.