What is called the inside area of closed lowercase letters?

The area referred to as the inside of closed lowercase letters is known as the counter. In typography, the counter refers specifically to the enclosed or partially enclosed space within a letterform. Common examples of letters that have counters include 'a', 'b', 'd', 'o', 'p', and 'q'. Each of these letters features a distinct space within their structure that is recognized as the counter. Understanding counters is essential for calligraphy and typography because they significantly influence the overall appearance and readability of written or printed text.

For instance, when designing letterforms, attention to the size and shape of the counter can affect how light and space interact in a font, ultimately impacting legibility and aesthetic appeal. It is also a key aspect of type design, as well as being critical in achieving balance and harmony in the overall composition of letterforms.