Deuterocanonical is a text related to Holy Scripture that comes from the Greek translation of the Septuagint (LXX) but not in the Hebrew canon.
The deuterocanonical books (meaning from the Greek “belonging to the second canon”) are books and passages considered by the Catholic Church, the Eastern Orthodox Church, the Oriental Orthodox Churches, and the Assyrian Church of the East as canonical books of the Old Testament, but which Protestant denominations consider apocryphal.

The modern Hebrew canon therefore does not include any of the seven deuterocanonical books, and this was the basis for excluding them from the Protestant Old Testament. The Septuagint translation of the Hebrew Bible into Greek, which the early Christian church used as the Old Testament, included all of the deuterocanonical books. The term distinguished these books from both the protocanonical books (the books of the Jewish canon) and the biblical apocrypha (books of Jewish origin that were sometimes read in Christian churches as scripture but were not considered canonical). The Council of Rome (382 A.D.) defined a list of books of Scripture as canonical, including most of the deuterocanonical books. Since the 16th century, most Protestant churches have accepted only the works of the Masoretic Text of the Hebrew Bible as the canonical Old Testament, and thus classify all non-canonical books of the Septuagint as apocryphal.