Okay kiddo, you know how you have your games and pictures on your kindle, right? Well, imagine if you had a lot of kindles, and you could access all of your games and pictures from any of them, even if you were in a different room or even a different city. That's kind of like what Cloud Atlas is, but instead of kindles, we're talking about really big computers called servers.
Cloud Atlas is a movie that tells a story about different people from different time periods and places who are all connected in some way, like how the different kindles would all be connected to your games and pictures. The movie was based on a book, which you might not have read yet, but that's okay because the movie is still really cool to watch.
But the concept of "cloud" comes from the idea that all of these people and their stories are connected through a "cloud" of shared experiences and ideas, which is kind of like the cloud that your games and pictures are stored in. So, when you hear people talking about Cloud Atlas, they're usually talking about the movie or the book that explores the idea of people being connected through a shared experience, like a cloud.