blue book

The term dates back to the 15th century, when large blue velvet-covered books were used for record-keeping by the Parliament of the United Kingdom.

blue book (plural blue books)

1. A book of statistics or almanac, usually published by an agency or as a trade publication.
   • 1912, Arthur Conan Doyle, The Lost World […], London, New York, N.Y.: Hodder and Stoughton, →OCLC:

     "I was the flail of the Lord up in those parts, I may tell you, though you won't find it in any Blue-book."

2. Used other than figuratively or idiomatically: see blue,‎ book.

• Project Blue Book
• blue book exam