Q. 1 What is the Apocrypha?
A. 1 It is the term under which is sometimes listed in the Protestant Holy Bibles the seven Books of the Old Testament that are found in the Catholic Holy Bible.
Q. 2 What are these seven Books of the Old Testament?
A. 2 They are the Books of Tobit, Judith, First and Second Maccabees, Wisdom, Sirach (sometimes called Ecclesiasticus), and Baruch (plus additions to Esther and Daniel).
Q. 3 Why do you say it is the term under which sometimes is listed...?
A. 3 As a general rule, the Protestant Holy Bibles contain only 66 Books while the Catholic Holy Bibles contain 73 Books, 46 in the Old Testament and 27 in the New Testament. When the Protestant Holy Bibles do list the additional seven Books, they are listed under the title of "Apocrypha" which means "hidden books.
Until the sixteen century, there was little disagreement about the Books of the Holy Bible. Around that time, Martin Luther (founder of the Lutheran Church) and other Protestant Churches rejected the established list of Books that were found in the Catholic Holy Bible.
Following this dissent, in 1546, the Council of Trent defined the Alexandrian list ( not the Palestinian list [Jewish]) of Books as the official list of Old Testament Books. At the same time, it reaffirmed the traditional list of New Testament Books. As such, today's Books that are contained in the Old Testament and the New Testament are the exact same Books that were defined at a number of Catholic Church Councils, namely at Rome in 382 A.D., at Hippo in 393 A.D. and at Carthage in 397 A.D.