In typography, ascenders are parts of letters that rise above the x-height.
Examples are the tall parts of b, d, f, and h.
The x-height is the height of the small (lower case) letter x. Letters that occupy no more than the x-height include a, c, e, and m. The imaginary line on which these letters sit is the baseline.
Parts of letters that hang below the baseline are called descenders. They occur in g, j, and p, for example.