Descender

The part of a letter that drops below the baseline, as in p or y. It gives type its lower depth, and leading its first constraint.

Descenders are why lines of type cannot simply stack: the tail of one line reaches into the territory of the next, and leading exists partly to keep them from touching. Their length is a design decision with consequences, long descenders are elegant and space-hungry, short ones sturdy and compact.

They also carry character: a y's tail can end in a straight cut, a curve or a flourish, and headlines set tight will interleave descenders and ascenders like fingers. We check the worst pair before committing a display setting; one collision reads as carelessness the whole page pays for.