Code BOOKDEAL25 applies 25% off of any printed book sold directly by Amazon.
Not valid on eBooks, Kindle Books, and audio books.
According to the terms, this discount can only apply once per Amazon account, expires on December 14 (today), and gives a maximum discount of $10.
So if you order a $20 book, the code will give $5 off.
If you order a $40+ book, the code will give $10 off.