In typography, a descender is the portion of a letter in a Latin-derived alphabet that extends below the baseline of a font.
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 most fonts, descenders are reserved for lowercase characters such as g, p, and y. Some fonts, however, also use descenders for some numerals (typically 3, 4, 5, 7, and 9). Such numerals are called old-style numerals. (Some italic fonts, such as Computer Modern italic, put a descender on the numeral 4 but not on any other numerals. Such fonts are not considered old-style.) Some fonts also use descenders for the tails on a few uppercase letters such as J and Q.
The parts of characters that extend above the x-height of a font are called ascenders.