Avesta (Zend). Lit., “the Law”. From the old Persian Âbastâ, “the law”. The sacred Scriptures of the Zoroastrians. Zend means in the “Zend-Avesta”—a “commentary” or “interpretation”. It is an error to regard “ Zend” as a language, as “it was applied only to explanatory texts, to the translations of the Avesta”(Darmsteter).
Source: H.P.Blavatsky - The Theosophical Glossary