The Bible is this big, kind of mysterious book. What is it? Kids just like you answer!
Maybe the best way to describe the Bible is the story of how God created the whole world, how it was broken by the bad things we've done, and how God is working to bring His Creation back to perfection through His Son Jesus and His people (Christians).
That's kinda a long way to describe it, but the Bible is a totally unique book! It was written by God through human writers, and it applies to everyone who's ever lived. (If you do have a shorter way to describe the Bible, I'd love to hear it.)
If you want to see a little bit longer answer to the question "What is the Bible?" then check out this video: