Is the earth flat?

Technically the Earth is an oblate spheroid but people saying the Earth is "round" is an accurate approximation. Since the Earth spins the poles become flattened and Earth bulges at the equator.

No planet can ever be flat. Gravity's tendency pulls everything toward a common center of the gravity's source. Even if the Earth started out flat, which it didn't, over time gravity would cause Earth to become more like a sphere.