Frontier

A frontier is like a big, invisible line where one area ends and another begins. Imagine you have a sandbox and a grassy area next to it. If you draw a line with your finger where the sand meets the grass, that's a frontier.

In the past, people used to explore and settle new lands, and as they did, they crossed frontiers. When they would go over these invisible lines, they would enter new places with new things to discover, like different animals, plants, and people. It was exciting, but also scary because they didn't know what was on the other side of the frontier.

Today, we still have frontiers in a way, but instead of exploring new lands, we often talk about frontiers in science or technology. For example, some scientists are trying to find a cure for cancer, and that would be crossing a frontier because it's something that hasn't been done before. It's exciting because it could change the world, but also scary because it's hard to do and might not work.