A Bible concordance is an alphabetical listings of words and phrases found in the Holy Bible and shows where the terms occur throughout all books of Scripture. With cross-references for verses, concordances make it easy to understand the meaning of terms and the context in which those words are used.
Catholic and Protestant Bibles both include 27 books in the New Testament. However, Catholic Bibles have an additional seven books in the Old Testament. The seven books included in Catholic Bibles are:
Catholic Bibles also include sections in the Books of Esther and Daniel which are not found in Protestant Bibles.
These are called the deuterocanonical books or the Apocrypha. The Catholic Church believes and teaches that these books are inspired by the Holy Spirit.
Early Christians read the Greek translation of the Old Testament, the Septuagint, that included these seven deuterocanonical books.
Retrieved from: http://www.usccb.org/bible/understanding-the-bible/faq.cfm
For more information, see The Canon of the Old Testament at New Advent's Catholic Encyclopedia