An elementary denotation of some symbolism, considered apart from its meaning. A letter is usually introduced into a reasoning by agreement, and is employed as an elementary "building stone" from which the expressions of a given symbolism are constructed in accordance with certain rules. These rules constitute the syntax of the symbolism. The interpretation of the expressions thus obtained forms the subject of the semantics of the symbolism.
A physical representation of a letter is sometimes called a "character" or "token" .
Letter. N.M. Nagornyi (originator), Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Letter&oldid=19267