"An" is an indefinite article used in the English language. It is used before words that begin with a vowel sound, such as "apple" or "hour." The purpose of "an" is to indicate that the noun it precedes is not specific or known to the reader. In contrast to "a," which is used before consonant sounds, "an" helps to create smoother pronunciation. For example, we say "an elephant" instead of "a elephant." This small word plays a crucial role in grammar, helping to clarify meaning and improve the flow of sentences.