Imagine you have a very long piece of paper, like a big ribbon. On this ribbon, there are many little pictures, all in a line. Each of these pictures shows something different, like a person walking, or a bird flying.
Now, let's pretend that this long piece of paper is inside a machine, kind of like a projector. When you turn on the machine, it pulls the paper ribbon through it really fast. As it pulls the ribbon through, it shines light on each picture, one at a time.
This happens so quickly that it looks like the pictures are moving! This is called a "filmstrip". It's like watching a mini-movie made of many little pictures.
Filmstrips were really popular a long time ago, before we had fancy movies with sound and color. But they were still really fun to watch! You could learn things, like about history or science, or just enjoy a good story.