Here is a breakdown of the different varieties of Scripture and other religious writings, and how our terms differ from the Protestants.
Canonical: all of the 66 books accepted by both Catholics and Protestants.
Deuterocanonical: (second canon) 7 books of the old testament that are part of the Septuagint and accepted as fully canonical by Catholics, but rejected by the Protestants, who call these books the Apocrypha (hidden). These books are Tobith, Judith, 1 and 2 Macabees, the Wisdom of Sirach, Wisdom, Baruch, and parts of Edith and Daniel. Protestants claim that St. Jerome, who translated the Vulgate, rejected these books, but they his comments out of context, and it wasn’t Jerome’s call anyway, he was a traslator, not a member of the ecuminical council that determined the canon.
Apocrypha (hidden): Works that are considered written or attributed to biblical people or men closely associated with them, but not considered divinely inspired. There is an excellent write-up in the Catholic Encylopedia here. There is also an excellent article about the differences, including the LDS take on the whole matter here.
Pseudepigrapha (things falsely written):a collection of early Jewish and some Jewish-Christian writings composed between c.200 B.C. and c.A.D. 200, not found in the Bible or rabbinic writings. These works are usually written anonymously. Excellent article and listing here.
Gnosticism (the way of knowledge): a sect of christianity, with some pre-christian roots that places the salvation of the soul merely in the possession of a quasi-intuitive knowledge of the mysteries of the universe and of magic formulae indicative of that knowledge. Gnostics were “people who knew”, and their knowledge at once constituted them a superior class of beings, whose present and future status was essentially different from that of those who, for whatever reason, did not know. Excellent Catholic perspective here.
Excellent secular write-up here. The most famous “Gnostic” writing is the famous “Gospel of Thomas” which was the subject of the movie Stigmata.