The set of letters used when writing in a language.

“In the first year of school, pupils are taught to recite the alphabet.”

A writing system in which letters represent phonemes. (Contrast e.g. logography, a writing system in which each character represents a word, and syllabary, in which each character represents a syllable.)

A typically finite set of distinguishable symbols.

“Let L be a regular language over the alphabet \Sigma.”

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