Filmizing is when you take something that was not originally made in a movie format, and turn it into a movie.
Imagine you have a big puzzle with a picture on it. It looks really cool, but it's just a picture. But then you decide you want to turn that picture into a movie. To do that, you have to take each piece of the puzzle and put it together in a certain order, so that it looks like the picture is moving.
That's what people do when they filmize something. They take a story or a book or a game or something else that's not a movie, and they figure out how to turn it into a movie. They take all the different parts of the story and put them together into a script. Then they film the actors saying and doing those things, and add music and special effects to make it look cool.
It's kind of like playing with Legos, where you take a bunch of different pieces and put them together to make something new. Except instead of Legos, the pieces are words, scenes, actors, and effects. And instead of making something you can hold in your hand, you make something you can watch on a screen!