TIL that they are Typographical terms.
They are typographical terms according to Wikipedia entries.
letter-spacing, also referred to as
trackingby typographers, refers to an optically consistent degree of increase (or sometimes decrease) of space between letters to affect visual density in a line or block of text.
-- Letter-spacing on Wikipedia
Remember it as "tracking spaces"
leadingrefers to the difference between the content height and the value of the
line-heightproperty. Half the leading is called the half-leading. User agents center glyphs vertically in an inline box, which adds half-leading on the top and bottom. For example, if a piece of text is "12pt" high and the line-height value is "14pt", 2pt of extra space should be added: 1pt above and 1pt below the text (this applies to empty boxes as well, as if the empty box contained zero-height text).
-- Leading on Wikipedia
Remember it as ??? Any good example?