Filler is like the cheese in macaroni and cheese. You know how the cheese is what makes the macaroni taste good and hold together? Well, filler is kind of like that but instead of macaroni, it's used in things like TV shows, movies, and books.
When TV shows or movies have a lot of filler, it means there are scenes or parts that aren't really necessary for the plot or story. It's like when you draw a picture and make the background really detailed even though it doesn't really matter for the main part of the picture.
For books, filler can be things like characters describing their thoughts and feelings too much, or repeating the same information over and over again. It's like when you write a story for school and your teacher says you need to add more details, but you just keep saying the same thing over and over again.
Overall, filler is used to make something longer or more detailed, but sometimes it's not always needed or necessary. It's kind of like adding extra sprinkles to your ice cream - it might look cool, but it doesn't actually make it taste any better.