Ground waves : These waves are radio waves of smaller frequencies which travel from one point on the surface of the earth to the other point on the surface of earth travelling along the surface of earth. With their help, the radio programs which are broadcasted in a limited area are broadcasted. These waves are known as ground waves.
Sky waves: Radio waves travel in straight lines and hence they are not able to travel long distances due spherical shape of the earth. If they are of smaller frequencies, they travel along the surface of the earth but if frequency is more, they are not able to travel to a large distance. Waves of higher frequency strike with the lower part of the ionosphere and reach larger distance on the earth. Since these waves come back from the sky and reach any place on earth, are known as sky waves.