The Old Testament was sometimes divided into The Law, The Prophets and the Psalms. Luke 24:44

The Law included the Pentateuch. The Prophets included the early historical books with the prophets. The Psalms were sometimes called the Writings and included all the rest of the books.

Among the rest of the books were six distinctly called Poetical books; namely Job, Psalms, Proverbs, Ecclesiates, Song of Solomon, and Lamentations.