What are the apocrypha?

Answer:

In the discourse of Catholic theologians the apocrypha are the secret writings which did not become part of the biblical canon, but who (can) claim to belong there because of their title or alleged origin (an Old Testament or New Testament person). [...] According to the understanding of the early Church apocryphal means the same as heretical; furthermore [it is] the term for books in the Septuagint [the Greek translation of the Hebrew Bible which was written during the second century by Christ at Alexandria, and which includes a number of additional books not included in the Canon of the Hebrew Bible] that were not included in the Jewish canon (Deuterocanonical). Protestant theology still calls them the apocrypha, whereas it calls all other Scriptures Pseudepigrapha) (Lexikon für Theologie und Kirche, Band 1 (1993), Spalten 824-825). Further information: Ph. Vielhauer, Geschichte der urchristlichen Literatur. Berlin, 1975, 485-718.