1. See upright. 1. horizontal. 1  being in a position or direction perpendicular to the plane of the horizon; upright; plumb. 2  of, pertaining to, or situated at the vertex. 3  Anatomyof or pertaining to the cranial vertex.
Last Updated: Radio wave, wave from the portion of the electromagnetic spectrum at lower frequencies than microwaves. The wavelengths of radio waves range from thousands of metres to 30 cm. These correspond to frequencies as low as 3 Hz and as high as 1 gigahertz (109 Hz).
Re: AM radio waves bounce off the ionospher, what do FM radio waves bounce off. Radio waves are the same thing as light waves. But the wavelength of radio waves is much longer. An AM radio wave has a wavelength in the range from 13 to 60 metres (shortwave) or around 200 to 500 metres (broadcast band).