What is "denkard"

The Dēnkard or Dēnkart ( Middle Persian: "Acts of Religion") is a 10th-century compendium of the Mazdaen Zoroastrian beliefs and customs. The Denkard is to a great extent an "Encyclopedia of Mazdaism" and is a most valuable source of information on the religion. The Denkard is not itself considered scripture.