X-heights, Ascenders, and Descenders
X-height refers to the height of the lower case letters in a line of text.
In the word man, the bottom of the letters forms the baseline, while the top forms the x-height. Ascenders are the parts of a letterform that extend above the x-height. In the word dismantle, the tops of the d, t, and l are the ascenders. Descenders extend below the baseline. In the word dismantling, the bottom of the letter g is the descender.