We listen to radios, we eat food heated in microwaves, we have X-rays taken of our broken bones. The entire range of energies of light, including both light we can see and light we cannot see, is called the electromagnetic spectrum . Because light is something that is given off, or radiated from an object, we can call it radiation. When we refer to the whole spectrum of light, we can call it electromagnetic radiation. Because we can see only visible light, we are put at a disadvantage because the Universe is actively emitting light at all different energies.
Light has different colors because it has different energies.
Of all the colors in the visible spectrum, red light is the least energetic and blue is the most. Beyond the red end of the visible part of the spectrum lie infrared and radio light, both of which have lower energy than visible light. Because of light's unique properties, it can be described not only in terms of its energy, but also its wavelength, or its frequency. This is a scientific convention that allows the use of the units that are the most convenient for describing whatever energy of light you are looking at. For example, it would be inconvenient to describe both low energy radio waves and high energy gamma-rays with the same units because the difference in their energies is so great.