Zoroastrian term for the literature written in Middle Persian to translate and explicate the Avestan scriptures. The supplementary explanations, which developed into the exegetical literature that we know from the Sasanian period and which are  preserved in the Middle Persian/Pahlavi texts are known as the Zand, hence the expression “Avesta and Zand” or “Zand-Avesta.”

See EXEGESIS i. In Zoroastrianism.