Simplify the following text for a Grade 4 native English-speaking person.
Original: The Islamic calendar or Muslim calendar or Hijri calendar ( ; at-taqw Ä `` m al-hijr Ä `` ; Persian : Ø Ù Ù Û Ù
Simplified: The Islamic calendar ( Arabic : Ø Ù Ø Ù Ù Ù Ù