Avestan is an umbrella term for two ancient Iranic languages: Old Avestan, spoken in the second millennium BCE, and Younger Avestan, spoken in the first millennium BCE. Despite the names, Younger Avestan is not thought to be a direct descendant of Old Avestan, but more like a “niece language”. Both types of Avestan are known from their conjoined use as scriptural languages in Zoroastrianism. The language was very similar to Vedic Sanskrit, as both are extremely ancient Indo-Iranian languages, less than a millennium removed from their common ancestor (Proto-Indo-Iranian).