The Book Of Shadows is a blank book that 'Wiccan' and 'Pagans' use. This is to write notes in, usually after carrying out a spell of some kind, and you would write how it went, how long it took to work, what to use and/or what not to use next time in the near future. It has nothing to do with Satanism, as far as I'm concerned.

One who has a mania for music.

The Wiccan book of rules, religious ceremonies, mythology, recipes, and spells. The text of this book differs from owner to owner, but physical description of being a book with a lock keeping it from being opened assured by all. A Book of Shadows can sometimes used by people outside of the Wiccan belief for keeping information.