The Tibetan Book of the Dead is one of the key scriptures in the Tibetan Buddhist belief system. It actually has nothing to do with Buddhism. The book deals entirely with local beliefs.
The book was originally written in Sanskrit, and it is called "BardoThötröl".
It is a guidebook for the process of death, known as the Bardo to Tibetans. A description of each stage of the Bardo, and eventually rebirth, is contained within its pages.
The book was meant to be read to someone who has just died, typically by a family member, student(if the deceased was a teacher), or close friend.