Have you ever found yourself not picking up the book because you were terrified of its size? I have, and I want that to change. From now on, I would dare myself to read two to three giant books a year and make it a challenge. It is always fun to tick off a prompt. 
I would consider books to be "giant" when they have 500+ pages. It is up to you to figure out your target page limits. 
This is the 2025 challenge edition!