Zend

The Zend or Zand (literally "interpretation"), refers to late middle Persian (see Pazend and Pahlavi) language commentaries on the individual books of the Avesta within Zoroastrianism. They date from the 3rd to 10th centuries and were not intended for use as theological texts by themselves but for religious instruction of the (by then) non-Avestan-speaking public. In contrast, the texts of the Avesta proper remained sacrosanct and continued to be recited in the Avestan language, which was considered a sacred language.