The Mathieu equation is like a big puzzle that tries to figure out how a certain type of wave behaves when it bounces around on a special kind of surface.
Imagine you have a really bouncy ball that you throw against a trampoline. The ball will bounce up and down in a certain pattern. Now imagine the trampoline is stretched in a special way so that there are hills and valleys on it. When you throw the ball on this trampoline, it will bounce in a different pattern than before.
The Mathieu equation tries to figure out exactly how the ball will bounce on this weird trampoline. But instead of a ball and trampoline, it's a special type of wave and a special type of surface.
Scientists study this equation because it helps them understand how certain things like electrons and sound waves move and behave in different situations. It's like a puzzle that helps them understand the world around us.