Okay kiddo, do you remember the movie where Tom Hanks' character got stuck on a deserted island all alone? Well, that's called being a castaway.
Being a castaway means being stranded somewhere without any other people or regular help around you. It can happen if you get lost in the woods or if you're on a deserted island like in the movie.
When you're a castaway, you have to figure out how to survive on your own because there's no one else to help you. You have to find food, make shelter, and get clean water to drink. It can be super scary and tough, but some people have been able to survive for months on their own.
So basically, being a castaway means being alone somewhere with no help, and you have to figure out how to survive on your own until you're rescued or find a way to get back to civilization.