surface wave or a ground wave can refer to a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. In radio transmission, a ground wave is a surface wave that propagates close to the surface of the Earth.
sky wave : Sky waves are reflections from the ionosphere.
Skywave is the propagation of radio waves bent (refracted) back to the Earth's surface by the ionosphere. As a result of skywave propagation, a night-time broadcast signal from a distant AM broadcasting or shortwave radio station (or rarely, a TV station) can sometimes be heard as clearly as local stations. Most long-distance HF radio communication (between 3 and 30 MHz) is a result of skywave propagation. For decades Amateur radio operators, limited to lower transmit power than commercial radio, have taken advantage of skywave for distance or DX communication.