A, An, & And: How to Choose the Right Word
https://www.thoughtco.com/a-an-and-1692639
"A" and "an" are indefinite articles that precede nouns or the adjectives modifying nouns. In English grammar, "a" and "an" are determiners, meaning they specify the identity or quantity of something, and for both words, that quantity is "one"—the word from which they're derived.
DA: 56 PA: 83 MOZ Rank: 44