Cel animation is a way of making movies or TV shows by drawing pictures on clear sheets of plastic, called cels.
Think of it like you have a big picture with a lot of characters, and you want to make them move around and talk. So, you draw each character in different poses and facial expressions on separate cels. Then, you stack the cels on top of each other in the same order they appear in the picture.
After that, you place them on a special camera that takes a picture of the top cel. Then you move the bottom cel just a little bit, and take another picture. You keep doing this over and over again, moving each cel just a little bit each time, until you have a lot of pictures in order.
When you play all the pictures in order, it makes it look like the characters are moving and talking! This is how they made old cartoons, like Bugs Bunny and Mickey Mouse. Nowadays, we can also use computers to help us make cel animations.