Book of Life

Definition

The "Book of Life" is where God has written the names of all the people whom God has redeemed and given eternal life.

Revelation describes the book as the "Lamb's Book of Life." This could be translated as "the book of life belonging to Jesus, the Lamb of God." The sacrifice of Jesus on the cross paid the penalty for people's sins so that they can have eternal life through faith in him.
The word for "book" can also mean "scroll" or "letter" or "writing" or "legal document."