The partially enclosed, somewhat rounded negative space in some characters.
Definition: The aperture is the partially enclosed, somewhat rounded negative space in some characters such as n, C, S, the lower part of e, or the upper part of a double-storey a.
Also Known As: counter
In typography, a counter or aperture is an area entirely or partially enclosed by a letter form or a symbol (the counter-space/ the hole of). Letters containing closed counters include A, B, D, O, P, Q, R, a, b, d, e, g, o, p, and q. Letters containing open counters include c, f, h, i, s etc. The digits 0, 4, 6, 8, and 9 also possess a counter.