Glossary » kerning
the amount of spacing between adjacent letters of type. It’s not sufficient to have letters equally spaced in order for them to look equally spaced. In a word like “balloon”, the letter pair “ll” must be further apart than the letter pair “oo” in order to appear evenly spaced. Letters should be adjusted by a principle of “optical spacing”, looking at how much whitespace is created between each letter pair and adjusting to make that amount of whitespace even throughout a word.
Most computer fonts have built-in kerning rules so that kerning rarely needs to be done by hand, but it may still be necessary for small fonts, unusually wide or tight spacing, or for logos and headlines where minor spacing problems will be more apparent. In very tight spacing, some letters may overlap, and this may require adjusting the individual letterforms to create a desirable appearance. Sometimes a principle called TNT, tight-no-touching, is used when tightening up words to move letters as close as possible without letters touching, but this will often result in poor optical spacing.