Okay kiddo, have you ever seen a globe? It's a round ball that shows all the countries and oceans of the world. But if you try to flatten the globe onto a piece of paper, it will get squished and stretched out. That's because the Earth is actually round and not flat like a pancake.
Now, scientists have measured the shape of the Earth and they found out that it's not a perfect sphere, but it's actually flattened at the top and bottom, like a slightly squished ball. This is called Earth flattening, or oblate spheroid.
Imagine you have a big ball of playdough that you push down on top and bottom with your hands. It will squish those parts and make the ball look flatter. That's what happened to the Earth, except it was squished by the force of gravity from the Sun and the Moon.
So even though the Earth looks flat when we stand on it and see the horizon, it's actually a big round ball that's slightly flattened at the top and bottom. Cool, huh?