Radio waves have a wavelength of >1mm and are the longest wavelength of electromagnetic radiation.
Radio waves are a type of electromagnetic radiation with wavelengths longer than infrared light in the electromagnetic spectrum. Travels at the speed of light.
They can occur naturally, but can also be made artificially. Radio waves are commonly used for broadcasting and radar and generally a fast method for communication. Other less common uses include usage in microwave ovens and MRI scans.
However, they can also be dangerous to humans at high power without proper shielding and requires lead to shield excessive radiation, e.g. next to a broadcasting tower. At lower power it is generally safe enough for widespread use.