What measurement relates lines of text in terms of vertical distance?

Leading refers to the vertical distance between lines of text. It is a typographical term that originated from the use of strips of lead to separate lines of type in traditional printing. When setting type, leading plays a crucial role in readability and aesthetic appearance, as it determines how crowded or spaced the text appears vertically.

In contrast, kerning involves the adjustment of space between individual characters to improve visual harmony. Font size indicates the size of the text itself but does not address the spacing between lines. Whitespace, or negative space, refers to the empty spaces around and between elements in a design, influencing layout but not specifically addressing the vertical relationship between lines of text. Thus, leading is the specific measurement that directly relates to the vertical distance of lines in a block of text.