This article relies largely or entirely on a single source. (December 2018)
Zend or Zand (Middle Persian: 𐭦𐭭𐭣) is a Zoroastrian technical term for exegetical glosses, paraphrases, commentaries and translations of the Avesta's texts. The term zand is a contraction of the Avestan language word zainti (𐬰𐬀𐬌𐬥𐬙𐬌', meaning "interpretation", or "as understood".
Zand glosses and commentaries exist in several languages, including in the Avestan language itself. These Avestan language exegeses sometimes accompany the original text being commented upon, but are more often elsewhere in the canon. An example of exegesis in the Avestan language itself includes Yasna 19-21, which is a set of three Younger Avestan commentaries on the three Gathic Avestan 'high prayers' of Yasna 27. Zand also appear to have once existed in a variety of Middle Iranian languages, but of these Middle Iranian commentaries, the Middle Persian zand is the only to survive fully, and is for this reason regarded as 'the' zand.
With the notable exception of the Yashts, almost all surviving Avestan texts have their Middle Persian zand, which in some manuscripts appear alongside (or interleaved with) the text being glossed. The practice of including non-Avestan commentaries alongside the Avestan texts led to two different misinterpretations in western scholarship of the term zand; these misunderstandings are described below. These glosses and commentaries 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 Avestan language texts remained sacrosanct and continued to be recited in the Avestan language, which was considered a sacred language. The Middle Persian zand can be subdivided into two subgroups, those of the surviving Avestan texts, and those of the lost Avestan texts.
A consistent exegetical procedure is evident in manuscripts in which the original Avestan and its zand coexist. The priestly scholars first translated the Avestan as literally as possible. In a second step, the priests then translated the Avestan idiomatically. In the final step, the idiomatic translation was complemented with explanations and commentaries, often of significant length, and occasionally with different authorities being cited.
Several important works in Middle Persian contain selections from the zand of Avestan texts, also of Avestan texts which have since been lost. Through comparison of selections from lost texts and from surviving texts, it has been possible to distinguish between the translations of Avestan works and the commentaries on them, and thus to some degree reconstruct the content of some of the lost texts. Among those texts is the Bundahishn, which has Zand-Agahih ("Knowledge from the Zand") as its subtitle and is crucial to the understanding of Zoroastrian cosmogony and eschatology. Another text, the Wizidagiha, "Selections (from the Zand)", by the 9th century priest Zadspram, is a key text for understanding Sassanid-era Zoroastrian orthodoxy. The Denkard, a 9th or 10th century text, includes extensive summaries and quotations of zand texts.
The priests' practice of including commentaries alongside the text being commented upon led to two different misunderstandings in 18th/19th century western scholarship:
Propagated by N. L. Westergaard's Zendavesta, or the religious books of the Zoroastrians (Copenhagen, 1852–54), by the early/mid 19th century, the confusion became too universal in Western scholarship to be easily reversed, and Zend-Avesta, although a misnomer, continued to be fashionable well into the 20th century.