Okay kiddo, let me tell you about the Earth radius. You know that the Earth is a big round ball that we live on, right? Well, the radius is like a line that goes from the center of the Earth to its edge. Imagine you have a big ball and you draw a line from the center to the outside. That line is its radius.
The Earth radius is a very special line because it helps us measure how big the Earth is. Scientists have measured the Earth's radius to be about 6,371 kilometers (or 3,959 miles). That's a really big number, isn't it?
But do you know what's cool? The Earth's radius is not the same all over the planet. The Earth is slightly flattened at the poles and bulges out at the equator, so the radius at the equator is a little bit longer than at the poles.
So, in summary, the Earth radius is a line that goes from the center to the edge of the Earth, and it helps us measure how big our planet is. Cool, right?