What is the term for the vertical space between lines of type?

The term for the vertical space between lines of type is leading. This typographical concept originates from the days of manual typesetting when thin strips of lead were used to create space between lines of text. Proper leading is essential for readability and aesthetic appeal in printed and digital text. It helps define the overall look of the text and can significantly impact how easily and comfortably the content can be read.

The other options refer to different typographical attributes: spacing generally refers to the overall space around characters or words; kerning specifically addresses the spacing between individual letter pairs to improve appearance and legibility; and tracking pertains to the uniform adjustment of space between multiple characters in a block of text, which can affect the density and readability at a larger scale. Understanding these distinctions is key in achieving effective typography in any design work.