According to the other meaning, primarily used by Catholics, it refers to those books from a similar period and in a similar style to the canonical books, but which none the less are not included in the Catholic canon (nor in the Protestant canon); Protestants call these books Pseudepigrapha?.
When refering to the Old Testament, Protestant Christians use the term Apocrypha to refer to a different set of books from what Catholic and Eastern Orthodox Christians do, who accept a fuller canon based on the Septuagint Greek version of the Old Testament in use by Greek-speaking Jews in the time of Jesus. The differences cover 7 books: Tobias, Judith, Baruch, Ecclesiasticus, Wisdom, First and Second Maccabees; and also certain additions to Esther and Daniel. When used by protesants, the term "Apocrypha" is used for the books that they reject but Catholics and Orthodox Christians accept, while they call books accepted by none of these groups "Pseudipigrapha". This term applies only to books in the Old Testament; in New Testament studies the two terms are used interchangeably.
We start with the Septuagint, the Greek translation of the Tanach (Hebrew Bible) that was made in Alexandria, Egypt, about [300 BC]?. This translation included a number of writings that the leaders of the Palestinian Jewish community eventually rejected as part of the Jewish biblical canon. These rejected works became known as the apocrypha; one of the main reasons that these works were rejected was because they were composed at a later date than all the other books which did make it into the Tanach. Most books in the apocrypha were composed between 200 BC and AD 100.
The books in the Septuagint, but not in the Hebrew version of the Bible, include the following:
The naming scheme of the Esdras books is complicated. The Tanakh (Hebrew Bible, aka Old Testament) has one book on this subject, called "Ezra-Nehemiah". Christians split this into two separate books, Ezra (called Esdras I by Catholics) and Nehemiah (called Esdras II by Catholics). This book (or books) is/are a canonical part of the Bible. However, two further books on the same subject are apocryphal, the first being called Esdras III (by Catholics), 1 Esdras (by Protestants), or Esdras A (by Greek Orthodox Christians). The second apocryphal book of Esdras is called Esdras IV (by Catholics), 2 Esdras (by Protestants) and Esdras B (by Greek Orthodox Christians).
Roman Catholic and Greek Orthodox churches regard the apocrypha as deuterocanonical, belonging to second-level biblical canon; they are deemed to be divinely inspired, but are of a lesser authority than the rest of the Bible. In contrast, most Protestant churches do not recognize the apocrypha as having any canonical status at all.
Texts rejected by orthodox Christian churches were also accepted by various Gnostic sects.
The Old Testament apocrypha - books accepted neither by Catholic, Protestant, nor Jewish readers - include a number of books with an apocalyptic? theme.
The New Testament apocrypha strictly defined - books accepted neither by Catholic nor Protestant readers - includes several extra gospels and lives of apostles. Some of these books were clearly produced by Gnostic authors or by members of other groups later defined as heterodox, or outside the body of the Church. Many of these writings were discovered in the 19th and 20th centuries, and have produced lively speculation about the state of affairs in Early Christianity.
While Jews reject the apocrypha as having religious value in and of of itself, at various times some in the Jewish community have drawn from it as a legitimate part of Jewish literary creativity; elements of the apocrypha have even been used as the basis for two important parts of the Jewish liturgy. In the Mahzor? (High Holy day prayer book), a medieval Jewish poet used [Ben Sira]? as the basis for a beautiful poem, Ke'Ohel HaNimtah?. This is a closing piyut? in the [Seder Avodah]? section, in the [Yom Kipur]? Musaf. It begins "How glorious indeed was the High Priest, when he safely left the Holy of Holies. Like the clearest canopy of Heaven was the dazzling countenance of the priest". (This can be seen, for example, on page 828 of the Birnbaum edition of the Mahzor.) The Conservative Mahzor replaces the medieval piyut with the relevant section from Ben Sira, which is more direct. The apocrypha has even formed the basis of the most important of all Jewish prayers, the Amidah? (the Shemonah Esrah). Ben Sira provides the vocabulary and framework for many of the Amidah's blessings, which were instituted by the men of the Great Assembly.