What Is Ascender?
An ascender is the part of a lowercase letter that rises above the x-height — the upper stems of letters like "b," "d," "h," "k," and "l." The height these reach is the ascender line. Ascenders and descenders give lowercase text its distinctive up-and-down silhouette, which aids reading.
Ascenders sometimes rise above the cap height, sometimes align with it — a deliberate design choice that affects a font's texture.
The word-shapes formed by ascenders and descenders help fluent readers recognise words at a glance, which is one reason all-caps text (which has neither) reads more slowly.