Glossary Term Definition
A single piece of type in metal typesetting; by extension, any individual character or glyph in a font.
Definition
In metal typesetting, a sort is an individual piece of type — a single physical block bearing one character. The term survives in the expression "out of sorts," meaning that the compositor has run out of a particular character. By extension, sort is used in digital typography to refer to any individual glyph or character within a font. A font's character set is its complete inventory of sorts. The term highlights the discrete, countable nature of the typographic alphabet — each letter, numeral, punctuation mark, and special character is a distinct sort.
Source
No access — Robert Bringhurst — p. 345:
A single letterform, or the matrix, pattern, or block used to reproduce it.