indefinite article

/IH0 N D EH1 F AH0 N AH0 T AA1 R T AH0 K AH0 L/
noun
  1. 1

    (grammar) A word preceding a noun to indicate that the noun refers to any member of the class of objects named by the noun.

Source: https://en.wiktionary.org/wiki/indefinite%20article