Okay kiddo, let me explain what a harmonic map is. Imagine you have a map of the world, just like the one you have on your wall. Now pretend you can stretch and bend that map in any way you want. A harmonic map is when you stretch and bend the map, but you don't change the way the distances between the different parts of the map relate to each other.
Let's break that down. When you stretch and bend the map, you might make some parts of it bigger and some parts smaller. But the important thing about a harmonic map is that the distances between the cities, mountains, and oceans on the map don't change. If you start off thinking that one city is 100 miles away from another, then after you stretch and bend the map, those two cities will still be 100 miles apart.
Why is this important? Well, sometimes mathematicians use harmonic maps to help understand things that are far more complicated than maps, like the way fluids or electrical charges move. By thinking about these things as if they were being stretched and bent like a map, mathematicians can try to understand their behavior in a simpler way. It's sort of like using a magnifying glass to look at a tiny bug up close - sometimes it helps to zoom in and simplify things in order to really understand what's going on.