Indefinite Article: A part of speech that is used to indicate a noun that is not specific, as opposed to a definite article like 'the' which refers to a specific noun.
Singular Noun: A noun that refers to one person, place, thing, or idea, as opposed to a plural noun which refers to more than one.
Vowel Sound: A speech sound produced by the relatively open configuration of the vocal tract, with vibration of the vocal cords, and without significant constriction or obstruction of the airflow.