Descender is a part of the letter which extends below the baseline, in the opposite way from ascender. Most of the descenders belong to lower-case characters, such as g, j, p, q and y. However, depending on the font, capital letters can also have descenders: usually we are speaking about Q and J. Some descenders are also called “tails” because of their curve: this works for letters j, y and Q, unlike the p and q where descenders are vertical. Letter g’s descender is often called “loop”. In some typefaces you can also notice the letter f with a descender. Many letters can slightly extend below the baseline but this is commonly known as overshoot, not to be mistaken for descender.
Descenders as elements have some varieties to be considered as well.
Crashing descenders. It happens when the descender of one letter touches the ascender of the letter on the line below. You may prevent it by providing more space between letters and lines with the adjustment of kerning, leading or tracking.
Numeral descenders. They are used in old style fonts for figures that have different positions and height. Try to avoid implementing these in tables as this kind of numerals can look messy. You may use it in big body text blocks for diversity.
Capital letters’ descenders. Usually this is about letter Q with its tail underneath the baseline and sometimes the letter J that outlines the baseline as well. You should check on potential crashing descenders when using these capital letters.