The indefinite article is a type of article used in English to refer to a non-specific noun. The two forms of the indefinite article are "a" and "an." "A" is used before words that begin with a consonant sound, while "an" is used before words that start with a vowel sound. For example, we say "a cat" and "an apple." Indefinite articles help indicate that the noun is not unique or previously mentioned. For instance, saying "I saw a dog" suggests any dog, not a specific one. This contrasts with the definite article "the," which refers to a specific item known to the listener.