google-fonts/cc-by-sa/knowledge/glossary/terms/counter/content.md

A counter, or counterform, is the transparent (negative or white) space enclosed inside a letterform. Counters can be closed, as in “o” and “d”, or open, as in “c” and “u.”


The name comes from the craft of traditional font production, in which a counterpunch makes indentations in the metal punch that is used for creating letter moulds. For more about this process, see the “Punchcutting” entry on Wikipedia.