The apocrypha is a selection of old books which were included in the 1611 version of the King James Bible inbetween the Old and New Testament. It was later removed in 1885 A.D. A portion of these apocrypha books have been called deuterocanonical books by the Catholic church and Church of the East.
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. This YouTube video shares an opinion for the apocrypha, and this website shares an opinion against. Both sides tend to cite the same verses that warn against adding or subtracting from the Bible: Revelation 22:18. The word 'apocrypha' literally 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 Scriputres, and yet are profitable and good to read." (King James Version Defended page 98.)