A

A may refer to several related concepts in language, writing, and science. Most commonly, it denotes the first letter of the Latin alphabet and the indefinite article used in English. The term also appears as a symbol or abbreviation across disciplines, in musical notation, mathematics, science, and everyday notation. This article outlines the main senses of “A” and “a” in their standard written forms.

As a letter, A is the first character of the Latin alphabet. Its earliest ancestors go back to the Phoenician letter aleph, which represented a glottal stop, passing through Greek alpha before arriving at the Latin form A. In English, the letter name is pronounced as “ay” (/eɪ/). The letter can represent a variety of phonemes in different contexts, including /æ/ as in cat, /eɪ/ as in make, and /ɑː/ as in father, depending on dialect and surrounding sounds. The uppercase form is A and the lowercase form is a, with typographic variants such as the single-storey and double-storey lowercase a in different fonts.

As an indefinite article, “a” marks a non-specific singular noun: a book, a idea. It is used before a consonant sound, whereas “an” is used before a vowel sound (e.g., an apple). Its origin lies in Old English as the numeral one, from which the indefinite article developed into its current general-use form. It is not used with plural nouns or proper nouns.

Beyond language, A is widely used as a symbol: in mathematics for area or matrices, in physics for the ampere unit, and in grading systems to denote high quality. It also appears as a variable or identifier in science, engineering, and notation systems.