In typography, the x-height refers to the distance between the baseline and the mean line in a typeface. Typically, this is the height of the lowercase letter x in the font; the source of the term. (Curved letters such as a, c, e, m etc. tend to exceed the x-height slightly.) However, in modern typography, the x-height is a design characteristic of the font and while an 'x' is usually matches the x-height, this may not always be the case.
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