The apocrypha is a selection of books which were published in the original 1611 King James Bible. These apocryphal books were positioned between the Old and New Testament (it also contained maps and geneologies). The apocrypha was a part of the KJV for 274 years until being removed in 1885 A.D. A portion of these books were called deuterocanonical books by some entities, such as the Catholic church.
Many claim the apocrypha should never have been included in the first place, raising doubt about its validity and believing it was not God-inspired (for instance, a reference about magic seems inconsistent with the rest of the Bible: Tobit chapter 6, verses 5-8). Others believe it is valid and that it should never have been removed- that it was considered part of the Bible for nearly 2,000 years before it was recently removed a little more than 100 years ago. Some say it was removed because of not finding the books in the original Hebrew manuscripts. Others claim it wasn't removed by the church, but by printers to cut costs in distributing Bibles in the United States. Both sides tend to cite the same verses that warn against adding or subtracting from the Bible: Revelation 22:18. The word 'apocrypha' means 'hidden.' Fragments of Dead Sea Scrolls dating back to before 70 A.D. contained parts of the apocrypha books in Hebrew, including Sirach and Tobit [source].
Keep this in mind when reading the following apocryphal books. Martin Luther said, "Apocrypha--that is, books which are not regarded as equal to the holy Scriptures, and yet are profitable and good to read." (King James Version Defended page 98.)