Slow motion is like watching a movie or a video in extra, extra, extra slow motion. It means the video is playing in a way that's slower than how it originally happened in real life.
Imagine you are at the playground and your friend jumps off the swing. You can see them jump in real time, meaning how things actually happen. But, if you watch your friend jump off the swing in slow motion, it looks like they're moving in slow motion, like a sloth.
Slow motion is really cool because it allows us to see things that happen too fast for our eyes to really see. It can help us learn how things work or even see the details of something that's happening too quickly to see in real life.