In typography, a descender is the portion of a letter that extends below the baseline of a font. The line that descenders reach down to is known as the beard line.
For example, in the letter y, the descender would be the “tail,” or that portion of the diagonal line which lies below the v created by the two lines converging. In the letter p, it is the stem reaching down past the o.
In most fonts, descenders are reserved for lowercase characters such as g, j, q, p, y, and sometimes f.
The parts of characters that extend above the x-height of a font are called ascenders.