 "Latter Prophets" (Isaiah, Jeremiah, Ezekiel, and "The Twelve" Minor Prophets; note that Jews do not include the Book of Daniel among the "Prophets," but in the following category).
Ketuvim (or Khetuvim) - meaning "Writings"; this "miscellaneous" group includes the books of Psalms, Job, Proverbs, Song of Solomon, and Ecclesiastes (called "Wisdom Literature" by Christians), the books of Ruth, Esther, Ezra, Nehemiah, and Chronicles (considered "Historical Books" in Christian Bibles), and the books of Daniel and Lamentations (placed among the "Prophets" in Christian Bibles).
Septuagint (LXX) - A collection of up to 53 books of ancient Jewish Scriptures written in Greek, including translations of all 24 books of the HB (Daniel, Esther, and Jeremiah are longer in the Greek versions than in the original Hebrew), as well as seven or more additional books (the "Deuterocanonical Books") that are not found in the HB. Several versions of the LXX have been preserved, some of which are slightly larger than others. The LXX was first translated and compiled around 250 BCE, probably in or near Alexandria, Egypt. The name "Septuagint" (meaning "seventy") comes from an ancient Jewish legend that tells how 70 (or 72) scholars translated the whole collection (or at least the Torah) in 70 days. All the books of the LXX were considered "scriptures" by most Greek-speaking Jews and early Christians; thus it became the basis of the Christian "Old Testament" (see below). In contrast to the three divisions and 24 books of the HB, the LXX rearranges, renames, subdivides, and/or expands some of the books, and adds several more books, thus resulting in up to 53 books in four main divisions:
Pentateuch (Greek, lit. "five scrolls") - the same five foundational books as in the "Torah" of the HB: Genesis, Exodus, Leviticus, Numbers, Deuteronomy.
Historical Books - includes not only the four "Former Prophets" of the HB (although two are subdivided and renamed: Joshua, Judges, 1 Kingdoms, 2 Kingdoms, 3 Kingdoms, 4 Kingdoms), but also several of the books categorized as "Writings" in the HB (Ruth, Esther, 1 & 2 Chronicles, Ezra, Nehemiah), and several books not found in the HB (Judith, Tobit, 1 & 2 Maccabees, and sometimes 1 Esdras and 3 & 4 Maccabees).
Poetic Books - includes some of the miscellaneous "Writings" of the HB (Psalms, Proverbs, Song of Solomon, Ecclesiastes, and Job) and several more books not found in the HB (Wisdom of Solomon, Sirach/Ecclesiasticus, and often Psalm 151, Odes, and Psalms of Solomon).
Prophetic Books - placed at the end as a fourth category; include not only the "Latter Prophets" of the HB (first the Minor Prophets, counted as 12 separate books, followed by the three Major Prophets: Isaiah, Jeremiah, Ezekiel), but also the books of Daniel and Lamentations (considered "Writings" in the HB), and a few other writings associated with Jeremiah and Daniel but not found in the HB (Baruch, Letter of Jeremiah, Susanna, Bel & the Dragon).
Deuterocanonical Books / OT Apocrypha - seven (or more) books that are in the LXX but not in the HB (Tobit, Judith, 1 & 2 Maccabees, Wisdom, Ecclesiasticus, Baruch - think of the mnemonic "T. J. McWEB"), as well as some additions to the books of Esther and Daniel (longer in LXX than in HB). These texts are considered part of the biblical canon by Orthodox and Catholic Christians (although recognized as later additions, and thus called "Deuterocanonical," meaning a "second canon"), but they are not considered canonical by Jews and most Protestant Christians today (who call them "Apocryphal"). Some Protestant Bibles include the Apocrypha in a separate section between the OT and NT; some Orthodox Bibles have even more books, which are not considered canonical by Catholics (1 & 2 Esdras, 3 & 4 Maccabees, Psalm 151, etc.).
Overview Chart: see my comparison of the arrangement of the HB/OT books in Jewish, Orthodox, Catholic, and Protestant versions of the Bible.
Shorthand Summary: LXX = the ancient Greek translation of HB books + the "Apocrypha" or "Deuterocanonical Books."
Non-Biblical Ancient Jewish Liter