Kerning

Every character carries its own side bearings — a little space to its left and right — and for most pairs those are enough. Some pairs are not most pairs. A capital A beside a capital V puts two diagonals back to back and opens a hole; a T followed by an o leaves the o stranded under the crossbar. Kerning is a table inside the font that says, for those specific pairs, move them this much closer or further apart.

It is per-pair, and that is the whole point. A well-made text face ships with hundreds or thousands of kern pairs, which is one of the things separating a professionally drawn font from one somebody made in an afternoon. It is also why kerning is not something you normally do by hand in body text: the font already did it, several thousand times, for every combination you are about to type.

Where you do it by hand is a logo or a headline — half a dozen letters, set once, at a size where every gap is visible. That is a different job from setting a paragraph and it is worth the hour.