Ground wave
From Amateur-radio-wiki
A ground wave is a radio wave that travels close to the surface of the earth. While it can technically reach beyond the horizon through diffraction and other propagation techniques, a ground wave is typically restricted by the curvature of the earth and cannot reach very long distances. There's a special area of expertise in amateur radio called DX or DXing that try to break those traditionnal limits and communicate further and further away with regular ground waves.
