What is full?

"Full means something can't hold anything else because it's packed tight."

Imagine you have a juice box. When it’s empty, you can pour juice into it until it’s all filled up, that’s when it becomes full. You can’t add more juice without spilling.

Think of a sandbox at the park. When it's empty, you can throw in as much sand as you want. But once it's all filled up to the top, no more sand will fit, that’s when the sandbox is full.

Your backpack is like a magic bag for your stuff. When it’s empty, you can put in books, toys, and snacks. But if you keep adding things, soon there's no room left, and that means your backpack is full!