The protocanonical books are those books of the Old Testament that are also included in the Hebrew Bible (the Tanakh) and that came to be considered canonical during the formational period of orthodox Christianity. The Old Testament is entirely rejected by some forms of Gnostic Christianity, but the Hebrew Bible was adhered to even more tightly by Jewish Christians than Gentile Christians. The term "protocanonical" is often used to contrast these books to the deuterocanonical books or apocrypha, which "were sometimes doubted" by some in the early church, and are considered non-canonical by most Protestants.