It is electromagnetic radiation, same as light. It travels at the speed of light in vacuum, and slightly slower in other media. The exact speed, as for light, depends on the frequency and the material properties. read more
It travels at the speed of light. This is exactly 299792458 m/s in a vacuum. In other mediums, such as atmosphere or open space, it travels slightly faster than visible light, but still less than 299792458 m/s. read more