Ascender

The stroke that rises above the x-height, as in b, d or k. With the descender it sets the vertical life of a line of text.

Ascenders give lowercase its skyline: the rhythm of rises above the x-height is much of what makes a word's silhouette recognisable, and silhouettes are how fluent readers actually read. Cover the top half of a line and reading stalls; cover the bottom and it mostly survives.

Their height relative to the capitals is a quiet stylistic marker, ascenders that overtop the caps read bookish and refined; equal heights read modern and plain. It matters where lines stack close: generous ascenders demand leading, and a tight lockup will force the choice between air and collision.