Answer:
The Apocrypha is a collection of books that were not canonized (that is, they were not included in the standardized list of books) in the Hebrew Bible (or Protestant Old Testament). The Catholic and Eastern Orthodox Church call these books Deuterocanonical and include them in their versions of the Old Testament. The books include Tobit, Judith, Additions to Esther, Wisdom of Solomon, Ecclesiasticus, Baruch, Additions to Daniel, 1 Maccabees, 2 Maccabees, 1 Esdras, and 2 Esdras.
Some editions of the Revised Standard Version (RSV) Bible include not only the Apocrypha listed above, but also the third and fourth books of Maccabees, Psalm 151, and the Letter of Jeremiah.