x-height

Def: En tipografía, la altura de una letra minúscula que no tiene trazos ascendentes ("b") o trazos descendentes ("p"); normalmente se toma como medida estándar la altura de la "x"
Ex: Its x-height was notably small, and the fount was equipped with many ligatures (tied letters) and with upright capitals; it was quickly and widely imitated.

(n.) = ojo medio, núcleo
Ex: Its x-height was notably small, and the fount was equipped with many ligatures (tied letters) and with upright capitals; it was quickly and widely imitated.