Electromagnetic radiation is classified depending on the amount of energy that it is able to carry on. The energy of an electromagnetic wave depends on its wavelength, and it can also be described in terms of the frequency of the wave.
Light, X-Rays, Infrared, Ultraviolet, Gamma rays, Radio waves, are all different kinds of electromagnetic radiation.
Visible light accounts only for a tiny fraction of the electromagnetic spectrum, which can be summarized as the following diagram shows.
As we can see, X-rays corresponds to wavelengths from 10^-11 to 10^-8 meters, or frequencies from approximately 10^16 to 10^20 Hz.
On the other hand, ultraviolet radiation corresponds to wavelengths form 10^-8 to 10^-7 meters, or frequencies from 10^15 to 10^16 Hz.
X-rays have higher frequencies than ultraviolet radiation, and then, x-rays carry more energy.