DifferencesTracking is letter spacing that doesn't consider the differences in how various shapes of glyphs fit together. It applies to all characters in a document, style, paragraph or other configured area of text. Kerning applies to ordered combinations of two characters. It is also possible for kerning to considered combinations of three or more characters but this is relatively rare. Negative kerning moves characters closer together and positive kerning moves them further apart. Kerning allows for characters to overlap if that looks good for a particular combination of characters.In the example above the kerning is designed to overlap the character pair "AV" because these characters slope away from each other. The user has overridden this overlap by setting a wide tracking.
|Tracking vs Kerning|
A constant letter spacing for a region of text.
A variable letter spacing that is specific to an ordered combination of characters in a particular font.