What do KERNING and LEADING mean>

Learning Center
Back when type was set by hand, there was a need for a new vocabulary.
In fact, we heard that the reason for calling letters "upper case" and "lower case" is that the capital letters were in the top drawer, and the little letters were in the lower drawer of the type case.
Kerning, which actually refers to the little serifs that extend beyond the letter's block shape, is subtracting space between characters to tighten them up, perhaps in order to draw up a single word, left as a "widow" on the last line onto a full line.
Tracking type is intentionally adding space, which a designer might do with the letters in a subhead. "Leading" refers back to bars of lead that spaced out lines of type--now it just means the spacing between the baselines (the imaginary line the type sits on).