Electromagnetic radiation is the propagation of electrical and magnetic waves through space.
Radio waves, light, X-rays and γ-radiation are all forms of this radiation.
The waves are described by a wavelength (λ) and a frequency (ν),
the product of which is equal to the speed of light.
The speed of light in vacuum is fixed to be equal to 299,792,458 m·s-1.
wavelength (λ) × frequency (ν) = speed of light (c)
Electromagnetic radiation can also be understood as a stream of photons
("light particles").
History
The Scottish mathematician and physicist James Clerk Maxwell (1831 - 1879)
has formulated the basic equations on which
the entire classical electromagnetic theory is built.