Simply put, in typography, tracking is a consistent increase (or decrease) in the amount of space between letters so as to alter the density in a line or block of text, whereas kerning is the process used to adjust spacing between a pair of individual letters to achieve a more visually appealing effect.
In other words, with tracking adjustments, letter spacing is even whereas with kerning adjustments spacing may vary between individual characters. To make manual adjustments, tracking is done across 2 or more letters, whereas kerning is done between 2 letters.
Tracking is often manually adjusted across a whole paragraph or lines of text where spacing between words is either too loose or too tight.
For example, if the word spacing in a line of justified text looks too loose, the tracking may be manually decreased on that line to allow an additional word to fit, or conversely, if the word spacing in a line of text is too tight, the tracking may be increased causing the last word to drop down to the next line. Often further adjustments may be needed within a block of text until letter spacing looks even across the entire paragraph.
{When I worked in newspaper and magazine publishing, I often had to adjust tracking on entire paragraphs while paginating the editorial pages.}
Kerning is usually manually adjusted between letters in words where a pair of abutting characters appear to have more or less space than the rest of the letters. For example, where the capital letters A and V appear next to each other, kerning may need to be adjusted between each letter until spacing looks consistent, even though the resulting character spacing between the A and V may overlap (see above “kerning” image).
{When designing ads, I often adjust the kerning between letters for a more visually appealing effect, although it’s usually after I’ve converted the text to outlines as I find this a lot easier.}
