The term "apocrypha" comes from the Greek word meaning "hidden" or "secret". Originally, the term was applied to sacred books whose contents were too exalted to be made available to the general public. Gradually, the term "apocrypha" took on a disparaging connotation, since the orthodoxy of these hidden books was often questionable.
"The Apocrypha" includes 15 books, all but one of which are Jewish in origin and found in the Septuagint (parts of 2 Esdras are possibly Christian and Latin in origin). Influenced by the Jewish canon of the OT, the custom arose of making the Apocrypha a separate section in the Protestant Bible, or sometimes even of omitting them entirely.
The Catholic view, expressed as a doctrine of faith at the Council of Trent, is that 12 of these 15 works (in a different enumeration, however) are canonical Scripture; they are called the Deuterocanonical Books. The three books of the Protestant Apocrypha that are not accepted by Catholics are 1-2 Esdras and the Prayer of Manasseh. Bible Study Tools offers popular apocrypha included in the Latin Vulgate, King James Version, and Revised Standard Version. Additional Deuterocanonical books are available in the Douay-Rheims Catholic Bible translation.