The set of letters used when writing in a language.

(Contrast e.g. logography, a writing system in which each character represents a word, and syllabary, in which each character represents a syllable.) A writing system that uses letters to represent consonant and vowel phonemes, contrasting with other writing systems such as abjad.

(computer science) A typically finite set of distinguishable symbols.

(India, Hong Kong, Singapore, Malaysia) An individual letter of an alphabet; an alphabetic character.

The simplest rudiments; elements.

(Internet slang, politics) An agent of the FBI, the CIA, or another such government agency.

(rare) To designate by the letters of the alphabet; to arrange alphabetically.