Descender is the anatomical name which refers to portions of certain letters that substantially descends below the baseline, extend further down then most other letters. The opposite of a descender is an ascender, both of which are types of extenders. Generally only lower-case letters poses descenders, like g, j, p, q, and y. However, some fonts render certain capital letters with descenders, most commonly Q, and at times J.
The descenders of certain letters have an allies. For example, the descenders of the letters j, y, and the capital Q are also called tails, because they curve or slant, unlike that of p and q which remain completely vertical. And that of the double-story g (see the image to the right) is also called a lobe or loop. Also, in many fonts, the lower-case f possesses a tail, or descender, when italicized.
In many fonts, small portions of many letters will subtly hang below the baseline (or above the x-height or cap height), but such is called an overshoot, and should not be mistaken for descenders or extenders.