Have you ever played dress-up with your friends or siblings? You put on different costumes and pretend to be someone else for a little while? That's kind of like what casting is in the performing arts!
When people make a movie or put on a play or musical, they need actors to play the different characters. Casting is the process of choosing which actors will play those parts.
Just like when you play dress-up, the people in charge of casting are looking for someone who looks and acts the part they need. For example, if they need someone to play a superhero, they might look for someone who is strong and fit. If they need someone to play a princess, they might look for someone who is graceful and elegant.
Sometimes, the people in charge of casting will even have the actors read lines or perform a scene to see if they are a good fit for the part. And just like when you play dress-up, sometimes the person who gets the part is the one who looks the most like the character, and sometimes it's the one who acts the part the best.
So, that's what casting is! It's like playing dress-up, but for grown-ups who get to pretend to be someone else on stage or on screen.