The word aperture comes from the Latin apertura, meaning opening, so it follows that, in typography, aperture would refer to an opening in a letter from. Specifically, it is the opening to the partially enclosed negative space (or counter) in characters such as a, c, e, n and s. Apertures can be small or large depending on the typeface. The lower case e of Berkeley Oldstyle Book has a large aperture due to the angle of the horizontal bar, but the e of Bembo Bold has a relatively small aperture. Vectora’s a has a tiny aperture, and while Serifa Light’s is larger, it is still small compared with that of Today Extra Light.