What is the Canon?

The word "canon" means "standard" or "rule." It is the list of authoritative and inspired Scriptures. Different religions have different canons.
In Judaism the canon consists of the books of the old Testament only.
In Protestant Christianity, the canon is the body of scripture comprised in the Bible consisting of the 39 books in the Old Testament and 27 in the New Testament.
In Roman Catholicism , additional books were added in 1546. These books are known as the apocryphal books: Tobit, Judith, 1 and 2 Maccabees, The Wisdom of Solomon, Ecclesiasticus (Sirach), and Baruch. I need to add here that Roman Catholicism maintains that the apocrypha was always inspired along with the Eastern Orthodox, Coptic and Armenian churches. The Protestant movement has not accepted the apocrypha.
In Mormonism , four additional books have been added to the Canon: The book of Mormon, the Book of Abraham, the Doctrine and Covenants, and the Pearl of Great Price.
In Christian Science an additional book has been added to the Canon. This additional book is called "Science and Health with Key to the Scriptures" written by Mary Baker Eddy.
In Islam , their inspired book is called the Quran.