The open space in a fully or partly closed area within a letter.
Definition: In typography, the enclosed or partially enclosed circular or curved negative space (white space) of some letters such as d, o, and s is the counter. The term counter may sometimes be used to refer only to closed space, while partially enclosed spaces in m, n, or h are the aperture. The shape and size of the counter and bowl (curved stroke enclosing the counter) can affect readability and is also an identifying factor for some typefaces.
Also Known As: aperture, inner space, enclosed space
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.