آن

In a sentence

• آن کتاب قدیمی است.

  That book is old.

  In this sentence, 'آن' is used as a demonstrative pronoun meaning 'that', referring to a specific book.

• مقاله او را درباره آن موضوع خواندم.

  I read her article about that subject.

  Here, 'آن' functions as a demonstrative adjective referring to a specific 'topic' or 'subject' mentioned previously.

• آن کمک زیادی کرد.

  That helped a lot.

  In this context, 'آن' is used as a pronoun referring to some previously mentioned aid or action.