The Apocrypha ("hidden", "doubtful") most commonly refers to a group of disputed books which are rejected by Protestants and most other Christian groups and accepted by the Roman Catholic organization.
So why are these books in the "Catholic Bible" and not in other Bibles?
The folks over at inplainsite.org have done a very good job of explaining the issues behind this debate. The article linked to below will answer such questions as:
-Did the Jews consider the Apocrypha part of the Old Testament?
-What did Jesus think of the Apocrypha?
-Does the New Testament refer to the Apocrypha?
-Did the early church fathers believe the Apocrypha was authoritative?
-What kinds of problems do we find with the Apocrypha?
For those who are curious about this topic I would encourage you to go read the article: