What is an ascender in typography?

In typography, an ascender refers specifically to the portion of a lowercase letter that extends above the x-height of a typeface. The x-height is the height of the lowercase letters, excluding ascenders and descenders. For example, in the letters "b," "d," and "h," the vertical strokes that rise above the x-height are considered ascenders. This aspect is crucial in type design as it affects the overall appearance, readability, and aesthetics of the font.

Understanding this allows designers to appreciate how ascenders can influence line spacing and the overall flow of text. The remaining choices, while related to aspects of letterforms, do not accurately define what an ascender is within the context of typography.