Electromagnetic radiation is the flow of energy at the speed of light through free space or through a material medium.
Electromagnetic radiation travels in electromagnetic waves, such as radio waves, visible light, and gamma rays. Electromagnetic waves are classified by wavelength. The longer the wavelength, the weaker the type of electromagnetic radiation, and the shorter the wavelength, the stronger the type of electromagnetic radiation. We call the strength of the wave, or the number of waves per second, frequency. The higher the frequency, the greater the affect on humans. Electromagnetic waves can as big as an atom's nucleus, buildings, or anywhere in between.
The electromagnetic spectrum
There are many different types of electromagnetic radiation, as can be seen above. These all fall onto a spectrum we call the electromagnetic spectrum. We humans see using a tiny part of this spectrum. We call these waves visible light. The longest waves of visible light are red light waves, and the shortest are purple. Anything longer than red waves we call infrared rays, and anything shorter than purple we call ultraviolet, or UV rays. Microwaves have lower frequencies than infrared waves, and radio waves' frequencies are even longer. These rays don't do as much damage to humans as rays shorter than violet light. X-rays are shorter than UV rays, meaning they have a higher frequency, and are therefore more dangerous. Gamma rays are the shortest and most dangerous type of electromagnetic wave. Gamma rays are so short, and their frequencies are so high, that they can penetrate and mutate cells.
In everyday life, we experience electromagnetic radiation every day. The sun is always radiating waves from the electromagnetic spectrum. Of those wastes, three are common. Those are ultraviolet radiation, visible light, and infrared radiation. Ozone in the stratosphere takes care of most ultraviolet radiation via the ozone oxygen cycle, and most infrared radiation is reflected by earth's atmosphere. That leaves visible light, the light we see with.