The term "apocrypha" is Greek for "hidden or secret (things)." When Jerome translated the Scriptures into Latin in the late fourth century, he noted that the Septuagint had many more books than the Hebrew Bible itself. Jerome called these "Apocrypha."

They are:

• The First Book of Esdras 
• Tobit (deuterocanonical)
• Judith (deuterocanonical)
• Additions to Esther (included in the Book of Esther in the Catholic Bible)
• The Wisdom of Solomon (deuterocanonical)
• Ecclesiasticus or the Wisdom of Jesus Son of Sirach (deuterocanonical)
• Baruch and The Letter of Jeremiah (deuterocanonical)
• Additions to Daniel: The Prayer of Azariah and The Song of the Three Jews, Daniel and Susanna, Daniel, Bel, and the Dragon (included in the Book of Daniel in the Catholic Bible)
• The Prayer of Manasseh
• The First Book of the Maccabees (deuterocanonical)
• The Second Book of the Maccabees (deuterocanonical)

Christians at the time of Christ and in the early Church read and quoted from the Septuagint Greek Bible, since the majority of Christians were Greek-speaking Gentiles. Jerome included these "apocryphal" books plus the Second Book of Esdras in his translation, the Vulgate, which became the standard Bible for nearly all of western Christendom until the Protestant Reformation of the sixteenth century. The Protestant Reformers decided to exclude the apocryphal books, on the basis that the shorter Hebrew Bible (thirty-nine books) was older and therefore more authoritative, and also because they disagreed with the Catholic Church, which relied in part on 2 Maccabees to defend the doctrines of purgatory and the saying of masses for the dead.

At the Council of Trent in 1546, the Catholic Church declared all the books in the Vulgate canonical, except for 1 and 2 Esdras and The Prayer of Manasseh. Thus, the Old Testament in the Catholic Bible consists of forty-six books, the thirty-nine from the Hebrew Bible being "protocanonical," while the seven from the Septuagint are called "deuterocanonical," i.e., a "second canon" of inspired books. 

To sum up, Protestants call "Apocrypha" the seven deuterocanonical books of the Catholic Old Testament, plus additional passages in the Books of Daniel and Esther, and other books found in the Vulgate but not in the Hebrew Bible. Catholics reserve the term "Apocrypha" for the books that Protestants called "Pseudepigrapha" (i.e., false writings, because most of these claim to be written by some great religious figure such as Moses or Enoch).