Apocrypha is a Greek word means hidden things.There are some people, especially the Catholics, who consider the Apocrypha also to be a part of The Bible.
About 12-15 books(and parts of books) found in greek orthodox and catholic OT,but not in Hebrew Bible or Protestant OT.
Protestants either ignore them or consider "deuterocanonical".
It is found in the middle section of the oxford bible. It is important for history of period between Ot and NT.