Okay kiddo, have you ever seen a really cool movie or TV show that had a really simple idea but was still really exciting and interesting to watch? That's called a "high concept." It's basically when someone comes up with one simple idea that is really easy to understand, but also really exciting and makes you want to know more.
For example, have you heard of the movie "Jaws"? It's about a giant shark that starts attacking people near a small town. That's it - that's the whole idea. But it's a really exciting idea that makes you want to know more - who will survive? How will they stop the shark? What other dangers will they face? That's what a high concept is - one simple idea that leads to lots of interesting questions and possibilities.
Lots of great movies and TV shows have high concepts. "The Hunger Games" is another example - it's about a group of kids who have to fight each other to the death in a futuristic society. "Jurassic Park" is about a theme park where dinosaurs are brought back to life, but of course things go wrong and the people have to fight for their lives.
So when someone talks about a high concept movie or TV show, they mean it's something really cool and exciting that is easy to understand and makes you want to know more. It's like a really good storybook that starts with a simple idea, but ends up being really exciting and interesting.