Definition of Letter spacing:
Adjustment applied to a block of text or paragraph, to increase or decrease the average distance between letters. In proportional letter spacing, the horizontal space between two characters is adjusted according to the contours of their shape. For example, the letter i will take less space than the letter m in the word main. In monotype letter spacing (used in older typewriters) the horizontal space between two characters is fixed, regardless of their shape or contours. Also called tracking.
Meaning of Letter spacing & Letter spacing Definition