So you know how sometimes people write stories and then print them in a book so you can read them anytime you want? Well, a doom book is kind of like that, but instead of a story, it's about some scary stuff that might happen in the future.
Here's the thing - sometimes people get worried about things happening in the world, like wars or diseases or anything else bad. And sometimes they write down what they think might happen if those things get really bad. That's what a doom book is - it's a bunch of ideas about what might happen if something really scary happens in the future.
Now, here's the important part: just because someone wrote something in a doom book doesn't mean it's definitely going to happen! It's kind of like a guess or a prediction - sometimes people are right, but sometimes they're wrong.
So yeah, that's what a doom book is - a book full of ideas about what might happen if things get really scary in the future. But remember, just because it's in a book doesn't mean it will definitely happen - things can always change.