It’s the visual spacing between letters, which usually involves some letters that have curves or corners to actually not strictly follow the spacing. For example the legs of the letter A might stick out a tiny bit in certain fonts. This gives text a more visually balanced kerning.
Damnit, I’m going to see this everywhere now, aren’t I?
Yep.
You’re welcome.
Relevant xkcd
Is kerning the spacing between letters?
It’s the visual spacing between letters, which usually involves some letters that have curves or corners to actually not strictly follow the spacing. For example the legs of the letter A might stick out a tiny bit in certain fonts. This gives text a more visually balanced kerning.
Between any typographical characters, but yeah, basically 🙂